I 


II 6  HISTOLOGY. 

The  usually  well-developed  externa  consists  of  intercrossing  bundles 
of  connective  tissue,  elastic  fibers,  and  longitudinally-disposed  smooth 
muscle-fibers,  that  are  more  highly  developed  in  the  veins  than  in  the 
arteries.  The  adventitia  of  certain  veins  (the  trunk  of  the  portal  and 

the  renal)  possesses  an  almost  com- 
intima.  --^crrr-^-:-__1;_^^         plete    membrane   of   longitudinally 

Media.  .^-~>_- -^_'-^ 

1  -ftc*"  ««-.  .*  .^riFs.  arranged  muscle-fibers  (Fig.  60). 

/     ^i..'  >(;^ ;;•,••;-•/•,..•,.     V-^V.      3*^  \        o  / 

Externa  with    cross-  * [?*$>**$$ 3  t  The  valves  of  the    veins   are 

sectioned   longitudi-  /         A*     '?  ",.•••  "•'- '« i  ^  3 /• 

nai  fibers,  folds     of    the     intima    covered   on 

\  -  '     -•.:-  ^.f-/-^ 

both     surfaces    by    epithelial-cells, 

FIG.  60. — CROSS-SECTION  OF  THE  RENAL  VEIN  OF        ,1  .1  r  j'  i     A 

MAN.   xso.   Techn.  NO.  35.  that     on    the   surface   directed   to- 

ward    the     vascular     stream     are 

elongated    in   the    direction    of  the  current ;   on    the   opposite    surface, 
toward  the  wall  of  the  vein,  they  are  transversely  elongated. 


THE  CAPILLARIES. 

The  capillaries  establish  the  communication  between  the  arteries  and 
veins.  There  are  a  few  exceptions,  as,  for  example,  in  the  corpora 
cavern osa  of  the  genital  organs.  The  transition  of  the  arteries  into  the 
capillaries  is  effected  by  a  gradual  simplification  of  the  structure  of  the 
vessel- wall  (Fig.  54).  The  media  becomes  steadily  thinner  and  finally  is 
represented  by  a  few  isolated  circularly-disposed  muscle-fibers  occurring 
at  wide  intervals,  that  ultimately  disappear.  The  externa  becomes  cor- 
respondingly attenuated  until  it  consists  of  a  thin  layer  of  connective 
tissue  containing  cells,  that  ultimately  also  vanishes,  so  that  at  last  the  only 
part  of  the  vessel-wall  that  remains  is  the  intima,  the  layers  of  which  are 
likewise  reduced  until  nothing  is  left  but  a  stratum  of  plate-like,  nucleated 
endothelial  cells.  Hence,  the  walls  of  the  capillaries  consist  of  a  simple 
layer  of  endothelial  cells,  the  form  of  which  may  be  most  aptly  com- 
pared with  a  steel  pen  pointed  at  both  ends.  These  cells  are  united  at 
their  edges  by  a  small  amount  of  cement-substance. 

The  capillaries  divide  without  decrease  in  caliber  and  by  anastomosis 
with  neighboring  capillaries  form  networks  differing  widely  in  the  size  of 
the  meshes.  The  closest  meshes  occur  in  the  capillary  networks  of 
secretory  organs,  for  example,  in  the  lung  and  liver  ;  wide-meshed  net- 
works occur  in  the  muscles,  the  serous  membranes,  the  special-sense 
organs.  The  reverse  obtains  in  regard  to  the  caliber  of  the  capillaries  ; 
the  widest  capillaries  are  found  in  the  liver,  the  narrowest  in  the  retina 
and  in  the  muscles. 

Development  of  Capillaries. — Only  the  developmental  processes  in 


THE    CIRCULATORY    SYSTEM.  II/ 

the  post-embryonic  epoch  will  be  considered  here.  A  minute,  conical, 
protoplasmic  mass  appears  on  the  wall  of  an  existing  capillary,  resting 
by  a  broad  base  on  the  latter  and  terminating  in  a  slender,  tapering,  free 
end.*  In  the  further  course  of  development  this  pointed  free  end  unites 
with  another  off-shoot  that  has  arisen  in  the  same  way  from  another  point 
on  the  capillary  wall.  These  formations  are  solid  at  first,  but  gradually 
become  hollow  by  an  extension  of  the  lumen  of  the  capillary,  and  sub- 
sequently the  walls  of  the  new  vessels  become  differentiated  to  endo- 
thelial  cells.  The  development  of  new  capillaries  is  always  consummated 
in  connection  with  existing  capillaries. 

All   medium   and  large   blood-vessels  possess  small   blood-vessels 


FIG.  61. — SURFACE  VIEW  OF  A  PORTION  OF  THE  GREATER  OMENTUM  OF  A  SEVEN-DAY-OI-D  RABBIT. 
c,  Blood-capiliaries,  some  containing  blood-corpuscles  ;  s,  capillary  sprout  tapering  to  a  free  solid 
point ;  /,  young  capillary,  the  greater  part  of  which  is  hollow,  at  s'  still  solid  ;  k,  nuclei  of  peritoneal 
endothelium.  X  240.  Techn.  No.  40. 

(vasa  vasorum)  that  provide  for  the  nutrition  of  their  walls  ;  they  run 
almost  exclusively  in  the  adventitia  (Fig.  56).  The  intima  always  is 
without  blood-vessels. 

All  blood-vessels  are  furnished  with  nerves,  which  form  a  plexus  of 
medullated  fibers  in  the  media  of  the  arteries  and  veins.  From  these, 
nonmedullated  fibers  arise  which  are  distributed  to  the  muscle-fibers. 
The  capillaries  are  accompanied  by  encircling  networks  of  delicate 
nonmedullated  nerve-fibers.  Many  blood-vessels  are  surrounded  by 
lymph-channels  ;  occasionally  the  lymph-spaces  in  the  adventitia  are  so 
wide  that  they  form  an  ensheathing  sinus  for  the  blood-vessel,  the 
adventitial  or  perivascular  lymph-space. 

*  Such  blind  capillary  sprouts  may  be  hollowed  out  at  an  early  period  ;  corpuscles  that 
happen  to  flow  into  them  disintegrate,  because  they  are  excluded  from  the  circulation  and  the 
interchange  of  gases,  and  fall  into  fragments  that  have  been  erroneously  interpreted  as  hemato- 
blasts;  they  have  no  connection  with  the  true  hematoblasts. 


Mm*  I>ib. 


i 


TEXT-BOOK 

OF 

H  ISTOLOGY 


STOHR 


/: 


TEXT-BOOK 


OF 


HISTOLOGY 


THE  MICROSCOPIC   TECHNIC 


BY 


DR.    PHILIPP    STOHR 

I'ROFKSSOR    OF    ANATOMY    AT    THE    UNIVERSITY    OF 


SECOND  AMERICAN  FROM  EIGHTH  GERMAN  EDITION 


TRANSLATED  BY  DR,   EMMA  L.   BILLSTEIN 

DIRECTOR  OF  THE  LABORATORIES  OF  HISTOLOGY  AND  EMBRYOLOGY,  WOMAN'S  MEDICAL  COLLEGE  OF  PENNSYLVANIA 

EDITED,  WITH  ADDITIONS 

BY 

DR.   ALFRED    SCHAPER 

DEMONSTRATOR    OF    HISTOLOGY    AND    EMBRYOLOGY,     HARVARD    MEDICAL    SCHOOL,     BOSTON,     MASS.;      FORME«LY 

DOCENT    OF    ANATOMY   AND    FIRST   ASSISTANT   AT   THE   ANATOMICAL    INSTITUTE 

OF    THE   UNIVERSITY    OF    ZURICH 


TKHitb  292  Illustrations    —  > 


PHILADELPHIA 

P.    BLAKISTON'S    SON    &    CO. 

IOI2      WALNUT     STREET 
1898 


7^- 


«  9fi  * 


COPYRIGHT,  1898,  BY  DR.  ALFRED  SCHAPER. 


PRESS  OF  WM.  F.  FELL  &  Co_, 
I22O-24  SANSOM  ST., 

PHILADELPHIA. 


INTRODUCTION. 


The  great  progress  of  medical  education  in  America  during  the 
past  twenty  years  is  marked  chiefly  by  the  increased  attention  given  to 
the  scientific  branches,  which  form  the  basis  of  all  medical  training  and 
practice.  In  no  respect  is  this  progress  more  obvious  than  in  the  recog- 
nition of  the  value  of  the  microscope  as  a  medical  instrument,  upon 
which  in  its  manifold  applications  to  anatomy,  physiology,  bacteriology, 
pathology,  and  sanitary  science  the  advance  of  medicine  depends  to  a 
far  greater  degree  than  upon  any  other  instrument  or  apparatus.  All 
these  applications,  however,  are  based  upon  a  knowledge  of  the  normal 
microscopic  anatomy,  or,  as  it  is  called,  the  histology  of  the  human  body. 
Thus  it  has  come  about  that  the  importance  of  histology  in  medical 
education  has  grown,  until  the  work  in  the  histological  laboratory  prob- 
ably equals  in  value  the  work  of  the  student  in  the  dissecting  room. 

These  circumstances  have  created  a  need  for  a  text-book  of  his- 
tology, combining  scientific  thoroughness  with  simplicity,  conciseness, 
and  clearness  of  exposition.  These  qualities  appear  to  me  felicitously 
combined  in  Stohr's  manual.  The  author's  style  is  singularly  clear  and 
succinct,  and  shows  unmistakably  that  it  is  based  upon  a  first-hand 
acquaintance  with  the  microscopical  pictures  of  the  various  tissues  and 
organs  to  be  described.  The  illustrations  are  of  a  very  high  order, 
both  for  their  faithfulness  to  the  actual  preparations  and  for  their  delicacy, 
and  this  delicacy  is  fully  preserved  in  the  present  edition  by  careful 
printing,  such  as  is,  unfortunately,  rare  in  American  text-books.  Pro- 
fessor Stohr  has  kept  constantly  abreast  with  progress  of  histological 
research,  and  thus  has  given  to  the  successive  editions  of  his  work  an 


18C281 


authoritative  value,  rendering  it  an  excellent  book  of  reference,  not  only 
for  students  but  for  others. 

The  translation  here  presented  is  very  faithful,  and  is  to  be  com- 
mended, especially  for  the  correct  rendering  of  the  technical  terms. 
The  character  of  the  original  has  been  preserved  scrupulously  ;  but  the 
editor  has  added  sixteen  figures  and  certain  notes,  as  well  as  a  chapter 
on  the  Uterus  and  Placenta,  which  will  be  found  to  add  to  the  usefulness 
of  the  volume  for  American  students. 

It  affords  me  pleasure  to  recommend  the  American  edition  of 
Stohr's  Histology  to  my  colleagues  and  to  students  of  medicine  and 
biology,  for  I  think  it  needs  only  to  become  known  to  secure  the  suc- 
cess which  its  many  merits  deserve. 

CHARLES  SEDGWICK  MINOT. 

HARVARD  MEDICAL  SCHOOL, 

August  29,  1898. 


EDITOR'S  PREFACE  TO  THE  SECOND  EDITION. 


The  favorable  acceptance  of  the  first  American  edition  of  Stohr's 
Text-book  of  Histology  has  apparently  proved  the  work  a  welcome 
addition  to  the  histological  literature  of  this  country.  In  preparing  a 
second  edition  the  editor  has  found  the  opportunity  to  revise  and  com- 
plete the  book  according  to  the  eighth,  very  much  enlarged,  German 
edition,  which  has  meanwhile  been  issued.  Therefore  the  present  Ameri- 
can edition  can  be  considered  as  offering  to  the  student  the  latest  results 
of  histological  research.  With  considerable  changes  and  additions  in 
the  text  twenty-one  new  illustrations  have  been  embodied  in  the  new- 
American  from  the  last  German  edition.  Beyond  this  the  editor  has 
ventured  to  add  ten  (Figs.  66,  76,  119,  131,  160,  172,  208,  209,  260,  265) 
illustrations  from  original  drawings,  hoping  to  contribute  further  to  the 
usefulness  of  the  book.  Some  new  editorial  remarks  and  additions 
appear,  mostly  in  the  form  of  foot-notes. 

The  editor  is  again  under  great  obligation  to  Dr.  E.  L.  Billstein 
for  a  thorough  and  very  successful  revision  of  the  English  translation, 
and  to  Prof.  Ph.  Stohr  for  placing  the  electrotypes  of  the  new  illustra- 
tions of  the  eighth  German  edition  at  his  disposal.  He  also  feels  deeply 
indebted  to  Messrs.  P.  Blakiston,  Son  &  Co.  for  the  excellent  reproduc- 
tion of  his  new  drawings  and  for  the  many  improvements  in  the  general 
arrangement  and  the  printing  of  the  work. 

ALFRED  SCHAPER. 
HARVARD  MEDICAL  SCHOOL, 
BOSTON,  MASS. , 


EDITOR'S  PREFACE. 


Stohr's  text-book  is  well  known  to  the  histologists  of  all  nations 
and  held  in  high  esteem  by  them.  To  the  German  medical  student  it 
has  become  an  indispensable  guide.  During  the  ten  years  of  its  exist- 
ence it  has  reached  an  extraordinary  sale  and  passed  through  six  revised 
editions.  It  has  been  translated  into  Italian  (1887),  French  (1890),  and 
Russian  (1891),  and  has  thus  come  into  the  hands  of  the  students  of 
these  nations.  These  facts  are  sufficient  to  guarantee  the  value  of  the 
work  without  further  recommendation.  Although  excellent  text-books 
of  Histology  already  exist  in  English,  still  the  peculiarity  and  special 
superiority  of  Stohr's  text-book  justifies,  in  our  opinion,  its  translation 
into  English  for  the  convenience  of  American  and  English  students.* 

It  is  especially  intended  for  the  use  of  students,  but  even  profes- 
sional histologists  and  physicians  will  find  in  it  much  valuable  informa- 
tion, as  well  as  suggestions  for  technical  purposes.  The  chief  merit  of 
the  work  lies,  on  the  one  hand,  in  the  brevity  and  perspicuity  of  the 
descriptive  text,  elucidated  by  illustrations  which  have  thus  far  never 
been  excelled  ;  and,  on  the  other  hand,  in  the  simplicity  and  certainty 
of  the  methods  for  preparing  the  most  important  microscopical  speci- 
mens. The  young  student  is  thus  enabled  to  practice  histological 
methods  privately,  at  a  minimum  cost,  in  connection  with  his  courses  in 
the  university.  The  preparation  of  almost  all  of  the  specimens  enu- 
merated in  the  book  can  be  made  simply  by  means  of  teasing,  isolation, 
or  cutting  with  the  razor,  but  those  students  who  have  a  microtome  at 
their  disposal  will  also  find,  in  an  Appendix,  brief  directions  for  the  pre- 
paratory treatment  (embedding  in  paraffin  and  celloidin)  of  specimens 
for  sectioning  with  the  microtome. 

With  the  permission  of  Prof.  Stohr  we  have  made  several  imma- 
terial, but  for  an  American  edition  very  desirable,  changes  in  the  text, 
and  have  considered  it  preferable  to  place  the  technical  part  as  a 
whole  at  the  end  of  the  book  rather  than  in  sections  after  the  several 


*In  1888  Stohr's  text-book  was  utilized  in  Kendrick's  Physiology,  but  in  such  a  frag- 
mentary form  and  so  intermingled  with  selections  from  other  authors  that  its  chief  merits  were 
entirely  lost.  This  use  of  the  book  can  not  be  considered  as  an  English  translation  proper. 

vii 


Vlll  EDITOR  S    PREFACE. 

chapters.  Furthermore,  we  have  enlarged  the  chapter  on  the  Uterus, 
in  order  to  give  detailed  consideration  to  the  various  functional  condi- 
tions of  the  organ,  and  added  to  the  book  an  entirely  new  chapter  on 
the  Placenta.  Eight  new  illustrations  (Figs.  229,  230,  232,  233,  234, 
236,  237,  238)  were  necessary  for  these  additions. 

The  editor  is  under  great  obligation  to  the  translator,  Dr.  Billstein, 
for  her  successful  efforts  in  reproducing  the  conciseness  and  clearness  of 
the  German  original.  Further,  he  desires  to  express  his  gratitude  to 
Prof.  Philipp  Stohr  for  placing  at  his  disposal  the  original  electrotypes, 
and  to  Drs.  Bohm  and  von  Davidoff  for  the  illustration  of  the  virginal 
uterus  (Fig.  229)  from  their  "  Lehrbuch  der  Histologie."  He  also  feels 
deeply  indebted  to  Prof.  Charles  S.  Minot  for  kind  assistance,  for  valuable 
criticism,  and  for  permission  to  use  two  illustrations  (Figs.  231  and  234) 
from  his  text-book  of  "  Human  Embryology"  ;  and,  finally,  to  Messrs. 
P.  Blakiston,  Son  &  Co.,  Philadelphia,  for  the  very  satisfactory  repro- 
duction of  the  new  drawings,  and  for  their  many  courtesies  during  the 

preparation  of  the  American  edition. 

ALFRED  SCHAPER. 
HARVARD  MEDICAL  SCHOOL, 
BOSTON,  June,  1896. 


CONTENTS. 


PART  I. 

GENERAL  TECHNIC. 


I.    THE    LABORATORY    APPOINT- 
MENTS,      

Instruments. 
Reagents. 

II.  THE  PREPARATION  OF  MICRO- 
SCOPIC SPECIMENS,  .... 

Introduction. 

Nature  of  the  Material. 

Killing  and  Dissecting  the  Ani- 
mals. 

Isolating. 

Fixation. 

Hardening. 

Decalcifying. 


17-25 


26-49 


The  Preparation  of  Microscopic  Speci- 
mens. — Continued. 

Sectioning. 

Staining. 

Injecting. 

Mounting  and  Preserving  of  the 
Preparations. 

Examination  of  Fresh  Objects. 

Storing  of    Permanent    Speci- 


III.   MANAGEMENT  OF  THE  MICRO- 
SCOPE,           50-54 

Drawing. 
Measurement. 


PART  II. 

MICROSCOPIC   ANATOMY. 


I.    HISTOLOGY. 


(Microscopic  Anatomy  of 

A. — CELLS, 55-64 

Parts  of  the  Cell. 

Form  of  Cells. 

Size  of  Cells. 

Vital  Properties  of  Cells. 

Phenomena  of  Motion  in  Cells 

Reproduction  and  Multiplication 

of  Cells. 

Phenomena  of  Secretion  in  Cells. 
Length  of  Life  of  Cells. 
Growth  of  Cells. 
Secretory  Products  of  Cells. 
Technic  No.  I. 
B. — TISSUES. 

I.    The  Epithelial  Tissues,    .    .       65-76 
Secretory  Activity  of  Epi- 
thelial Tissues. 


the  Cells  and  the  Tissues.) 
Tissues. — Contimied. 
The  Glands. 
Technic  No.  2. 

II.    The  Supporting  Tissues,  .    .    .       76-90 
Connective  Tissue. 
Cartilage. 
Bone. 
Technic  No.  3-19. 

III.  The  Muscular  Tissues 9^-97 

Smooth  Muscle-Tissue. 
Striated  Muscle-Tissue. 
Technic  No.  20-26. 

IV.  The  Nervous  Tissues,  ....     97-108 

Nerve-Cells. 
Nerve-P'ibers. 
Technic  No.  27-34. 


IX 


CONTENTS. 


II.    MICROSCOPIC  ANATOMY  OF  THE  ORGANS. 


I.    THE  CIRCULATORY  SYSTEM,  .  109-137 

1.  The  Blood- Vessel  System,  .   109-121 

The  Heart. 

The  Arteries. 

The  Veins. 

The  Capillaries. 

Development  of  Capil- 
laries. 

Glomus  caroticum  and  coc- 
cygeum. 

The  Blood. 

Development  of  Colored 
Blood-corpuscles. 

2.  The  Lymphatic  System,  .    .   121-129 

The  Lymph-vessels. 

The  Lymph-glands. 

The  Peripheral  Lymph- 
nodules. 

The  Lymph. 
The  Spleen. 
Technic  No.  35-56,      ....   129-137 

II.    THE  ORGANS  OF  THE  SKELE- 
TAL SYSTEM,     137-156 

The  Bones. 

The  Articulations. 
The  Cartilages. 
Development  of  Bone. 
Development   of    Primary 

Bone. 

Development  of  Second- 
ary or  Intermembranous 
Bone. 

Growth  of  Bone. 
Resorption  of  Bone. 
Technic  No.  57-62,  .    .    .    152-156 

III.   THE  ORGANS  OF  THE  MUSCU- 
LAR SYSTEM, 157-161 

The  Muscles. 

The  Tendons. 

The  Fasciae. 

Tendon-sheaths  and  Bursae. 

Technic  No.  63-67, 160-161 

IV.  THE  ORGANS  OF   THE  NER- 
VOUS SYSTEM, 162-207 

I.  The  Central  Nervous  System,   162-185 
The  Spinal  Cord. 
Topography. 
Minute  Structure. 


The  Organs  of  the  Nervous  System. 

—  Continued. 
The  Brain. 

The  Cerebral  Cortex. 
The  Cerebral  Ganglia. 
The  Gray  Substance  of 

the  Ventricles. 
The  Cerebellar  Cortex. 
The  White  Substance. 
The    Hypophysis    Cere- 

bri. 

The  Epiphysis. 
The    Membranes    of    the 
Central  Nervous  System. 
The    Blood  -  vessels    and 
Lymph-vessels    of    the 
Central  Nervous  System. 
2.  The  Peripheral  Nervous  Sys- 
tem,         .    .   185-198 

The  Nerves. 
The  Ganglia. 
The  Peripheral  Nerve  End- 
ings. 
Terminations  of  Sensory 

Nerves. 
Terminations   of  Motor 

Nerves. 

The  Suprarenal  Body. 
Technic  No.  67-89, 199-207 

V.   THE  DIGESTIVE  ORGANS,    .    .  208-265 

Mucous  Membranes. 

The  Mucous  Membrane  of  the 
Oral  Cavity. 

The  Teeth. 

Development  of  the  Teeth. 

The  Tongue. 

The  Pharynx. 

The  Esophagus. 

The  Stomach. 

The  Intestines. 

The  Blood-vessels  of  the  Stom- 
ach and  Intestines. 

The  Lymph-vessels  of  the  Stom- 
ach and  Intestines. 

The  Nerves  of  the  Stomach  and 
Intestines. 

The  Salivary  Glands. 

The  Liver. 

The  Peritoneum. 

Technic  No.  90-120,     ....   255-265 


CONTENTS. 


XI 


PAGE 

VI.  THE  RESPIRATORY  ORGANS,  266-276 
The  Larynx. 
The  Trachea. 

The  Bronchi  and  the  Lungs. 
The  Thyroid  Gland. 
The  Thymus  Body. 
Technic  No.  122-128,    .    .    .    274-276 

VII.  THE  URINARY  ORGANS,    .   .  277-288 
The  Kidneys. 
The  Ureters. 
The  Urinary  Bladder. 
The  Urethra. 
Technic  No.  129-139,   .    .    .   286-288 

VIII.  THE  REPRODUCTIVE  ORGANS,  289-320 
The  Male  Reproductive  Or- 
gans. 

The  Testicle. 

The  Semen. 

The  Excretory  Ducts  of 

the  Testicle. 
The  Prostate  Body. 
The  Penis. 

The  Female  Reproductive  Or- 
gans. 

The  Ovaries. 

The  Oviduct. 

The  Uterus. 

The  Placenta. 

The  Vagina  and  the  Gen- 

italia. 
Technic  No.  140-155,   .    .    .   318-320 

IX.  THE  SKIN  AND  ITS  APPEND- 
AGES,    32I~34o 

The  Skin. 

The  Nails. 

The  Hairs  and  the  Hair  Fol- 
licles. 

Development  of  the  Hair. 

Growth  of  the  Hair  and  of  the 
Root-sheaths. 

Shedding  and  Replacement  of 
Hair. 

The  Glands  of  the  Skin. 

The  Blood-vessels,  Lymph- 
vessels,  and  Nerves  of  the 
Skin. 

The  Mammary  Glands. 

Technic  No.  156-168,    .    .    .   337-34° 


X.  THE  EYE  AND  ITS  APPEND- 
AGES,      34I-376 

The  Eyeball. 

The  Tunica  Externa. 
The  Cornea. 
The  Sclera. 

The  Tunica  Media. 
The  Choroid. 
The  Ciliary  Body. 
The  Iris. 

The  Irido-corneal  Angle. 

The  Tunica  Interna. 

1.  Pars  Optica  Retinae. 
The  Cerebral  Layer. 
The     Neuro  -  epithelial 

Layer. 

The  Pigmented  Epithe- 
lium. 

The  Macula  and  Fovea 
Centralis. 

The  Ora  Serrata. 

2.  Pars  Ciliaris  Retinae. 

3.  Pars  Iridica  Retinae. 
The  Optic  Nerve. 

The  Lens. 

The  Vitreous  Body. 

The  Suspensory  Ligament. 

The  Blood-vessels  of  the  Eye- 
ball. 

The  Lymph-channels  of  the 
Eyeball. 

The  Nerves  of  the  Eyeball. 

The  Eyelids. 

The  Lacrymal  Glands. 

Technic  No.  169-185,    .    .    .   369-376 

XL  THE  ORGAN  OF  HEARING,  .  377 -392 
The  Internal  Ear. 

The   Saccule,  Utricle,  and 

Semicircular  Canals. 
The  Cochlea. 
The  Middle  Ear. 

The  Tympanic  Cavity. 
The  Eustachian  Tube. 
The  External  Ear. 
The  Tympanum. 
The      External     'Auditory 

Canal. 
Technic  No.  186-191,    .    .    .  39°-392 

XII.  THE  OLFACTORY  ORGAN,   .  393~398 
The  Vestibular  Region. 


Xll 


CONTENTS. 


The  Olfactory  Organ. — Continued, 
The  Respiratory  Region. 
The  Olfactory  Region. 
Technic  No.  192-195,    .    . 


397 


XIII.  THE  TASTE-BUDS,     . 
Technic  No.  196-199, 


PAGE 

399-402 

401 


APPENDIX. 


MICROTOME  TECHNIC, 403-410 

I.  Microtome. 
II.   Embedding. 

The  Paraffin  Method. 
The  Celloidin  Method. 
III.   Sectioning. 

Paraffin  Objects. 

With    the    knife   placed     . 
obliquely. 


Microtome  Technic. — Continued, 

With    the    knife   placed 

transversely. 
Obstacles   in    Sectioning 

and  their  Remedy. 
Celloidin  Objects. 
IV.   Preservation  of  Sections. 
Paraffin  Objects. 
Celloidin  Objects. 
INDEX, 


413 


LIST  OF  ILLUSTRATIONS. 


FIG.  PAGE 

1.  Leitz  Microscope, 51 

2.  Diagram  of  a  Cell, 57 

3.  Cell  of  Bone-Marrow  of  Rabbit, 58 

4.  Leucocytes  of  Frog, ....  59 

5.  Karyokinetic  Figures — Epithelium  of  Salamander,  .    .    . 6l 

6.  Nuclear  Structure,  Connective-Tissue  Cell, 64 

7.  Epithelial  Cells  of  Rabbit,  Isolated, 65 

8.  Pigmented  Epithelium, 66 

9.  Simple  Columnar  Epithelium, 66 

10.  Stratified  Squamous  Epithelium, 66 

11.  Stratified  Ciliated  Epithelium, 67 

12.  Terminal  Bars,  Colummar  Epithelium, 68 

13.  Scheme  of  the  Network  of  Terminal  Bars, 68 

14.  Prickle-Cells, 68 

15.  Secreting  Epithelial-Cells, 69 

1 6.  Crypt  of  Lieberkiihn, 7° 

17.  Diagram  of  the  Different  Gland-Forms, 72 

1 8.  Mucous  Glands  of  Tongue  of  Rabbit, 74 

19.  Fundus  Gland  of  Mouse,      74 

20.  Diagram  of  the  Origin  of  Crescents, 75 

21.  Umbilical  Cord  of  Human  Embryo, 76 

22.  Connective-Tissue  Bundles, 76 

23.  Elastic  Fibers, 77 

24.  Network  of  Elastic  Fibers,  passing  into  a  Fenestrated  Membrane, 78 

25.  Connective-Tissue  Cells,  Bundles  of  Connective-Tissue  Fibers,  Plasma  Cells,    .    .  78 

26.  Fat-Cells, 79 

27.  Adipose  Tissue,      79 

28.  Serous  Fat-Cells, 80 

29.  A  Piece  of  the  Greater  Omentum  of  Man, 8l 

30.  Reticular  Connective  Tissue, 81 

31.  Hyaline  Cartilage, 82 

32.  Elastic  Cartilage, 83 

33.  Section  of  Intervertebral  Disc  of  Man 84 

34.  Ground  Section  of  Dried  Bone  of  Adult  Man, 85 

35.  Sections  of  Humerus  of  Human  Embryo  and  of  Middle  Turbinal  Bone  of  Man,    .  85 

36.  Section  of  Diaphysis  of  Humerus  of  Human  Embryo, 86 

37.  Adipose  Tissue,  Human  Scalp, 88 

38.  Smooth  Muscle-Fibers,  Small  Intestine  of  Frog, 90 

39.  Intercellular  Bridges  of  Smooth  Muscle-Fibers, 91 

40.  Intercellular  Bridges  in  Section ;    Smooth   Muscle-Fibers  of  Human  Intestine  in 

Transverse  Section, 91 

41.  Striated  Muscle-Fibers  of  Man, 93 

42.  Isolated  Striated  Muscle- Fibers  of  Frog, 94 

43.  Muscle-Fibers  of  Heart, 95 

44.  Diagram  of  a  Neuron, 98 

45.  Various  Forms  of  Ganglion -Cells, 99 

46.  Multipolar  Nerve-Cells, 100 

xiii 


XIV  LIST    OF    ILLUSTRATIONS. 

FIG.  PAGE 

47.  Cell  of  Purkinje, 101 

48.  Nerve-Cells  from  the  Spinal  Cord  of  an  Embryo  Chick, 102 

49.  Teased  Preparation  of  the  Sympathetic  Nerve  of  Rabbit, 103 

50.  Medullated  Nerve-Fibers, 104 

51.  Medullated  Nerve-Fibers,  treated  with  Silver  Nitrate  Solution, 105 

52.  Nerve-Fiber,  showing  a  Node  of  Ranvier, 107 

53.  Papillary  Muscle  of  Human  Heart, 109 

54.  Small  Arteries  of  Man, no 

55.  Endothelium  of  a  Mesenteric  Artery,       ..             Ill 

56.  Cross-Section  of  the  Brachial  Artery  of  Man, 112 

57.  Cross-Section  of  the  Thoracic  Aorta  of  Man, 113 

58.  Cross-Section  of  a  Human  Vein, 114 

59.  Elastic  Fibers  of  a  Human  Vein, 115 

60.  Section  of  the  Renal  Vein  of  Man, 116 

61.  Developing  Capillaries  in  the  Omentum  of  a  Rabbit, 118 

62.  Human  Blood-Corpuscles  ;  Amphibian  Blood- Corpuscles, 118 

63.  Colorless  Blood-Cells  of  Man, 119 

64.  Hemin  and  Hematoidin  Crystals  of  Man ;   Hemoglobin  Crystals  of  a  Dog,      ...  120 

65.  Lymph-Vessel  from  the  Mesentery  of  a  Rabbit, 121 

66.  Section  of  Lymph-Gland  of  a  Rabbit, 123 

67.  Section  of  the  Medulla  of  a  Lymph-Nodule  of  an  Ox, 124 

68.  Cross-Section  of  Human  Spleen, 126 

69.  Elements  of  Human  Spleen,     .    . 127 

70.  Reticular  Connective  Tissue  of  Human  Spleen, 127 

71.  Three  Karyomitotic  Figures  from  Spleen  of  Dog, 127 

72.  Section  of  Spleen  of  Mouse, 126 

73.  A.     Section  of  Injected  Spleen  of  Cat, 128 

73.  B.     Schematic  Drawing  of  Section  62,  A, 128 

74.  Longitudinal  Section  of  a  Human  Metacarpus,      138 

75.  Cross-Section  of  a  Human  Metacarpus, 139 

76.  Section  of  Bone-Marrow  of  Rabbit, 140 

77.  Elements  of  Human  Bone-Marrow, 141 

78.  Cross-Section  of  the  Femur  of  Adult  Man, 141 

79.  Vertical  Section  of  the  Head  of  a  Metacarpus  of  Adult  Man, 143 

80.  Synovial  Villi  from  a  Human  Knee-joint, 144 

81.  Section  of  the  Great  Toe  of  a  Human  Embryo  Four  Months  Old, 146 

82.  Section  of  the  Finger  of  a  Human  Embryo  Four  Months  Old, 147 

83.  Longitudinal  Section  of  the  Phalanx  of  the  First  Finger  of  a  Human  Embryo,  .    .  148 

84.  Cross-Section  of  the  Upper  Half  of  the  Shaft  of  the  Humerus  of  a  Human  Embryo,  149 

85.  Cross-Section  of  the  Lower  Jaw  of  a  Newborn  Dog, 15° 

86.  Horizontal  Section  of  the  Parietal  Bone  of  a  Human  Embryo,  . 151 

87.  Osteoclasts  and  Howship's  Lacunae, I52 

88.  Elements  of  the  Fresh  Bone-Marrow  of  a  Calf, 153 

89.  Cross-Section  of  the  Adductor  Muscle  of  a  Rabbit,      157 

90.  Cross-Section  of  Dried  Human  Tendon, 158 

91.  Tendons  of  a  Rat's  Tail, 159 

92.  Section  of  the  Gastrocnemius  Muscle  of  a  Frog,      159 

93.  Cross-Section  of  the  Cervical  Enlargement  of  the  Human  Spinal  Cord, 163 

94.  Motor  Nerve-Cells  from  the  Spinal  Cord  of  a  Rabbit, 165 

95.  Cross-Section  of  the  Spinal  Cord  of  an  Embryo  Chick, 166 

96.  Scheme  of  the  Spinal  Cord,     . 167 

97.  Longitudinal  Section  of  the  Spinal  Cord  of  a  Rabbit,      168 

98.  Section  of  the  Spinal  Cord  of  a  Rat,  showing  Collaterals, 169 


LIST    OF    ILLUSTRATIONS.  XV 

FIG.  PAGE 

99.     Glia-Cells  from  the  Spinal  Cord,      170 

100.  Cross-Section  of  the  Lateral  Column  of  a  Human  Spinal  Cord, 171 

101.  Vertical  Section  of  the  Human  Cerebral  Cortex, 173 

102.  Scheme  of  the  Cerebral  Cortex,       173 

103.  Pyramidal  Cell  from  the  Cerebral  Cortex  of  Adult  Man,  .......  .    .  174 

104.  Glia-Cells  from  the  Brain  of  Man, 175 

105.  Section  through  the  Cerebellar  Cortex  of  Adult  Man, 177 

106.  Small  Granule-Cell  from  the  Cerebellar  Cortex  of  a  Kitten, 177 

107.  Large  Granule-Cell  from  the  Cerebellar  Cortex  of  a  Kitten, 177 

108.  Cell  of  Purkinje  from  the  Human  Cerebellar  Cortex, 178 

109.  Scheme  of  the  Cerebellar  Cortex, 179 

no.     Basket-Cell  for  the  Cerebellar  Cortex  of  a  Cat, 180 

in.     Section  of  the  Cerebellar  Cortex  of  Adult  Man, 181 

112.  Glia-Cells  of  the  Cerebellar  Cortex  of  Adult  Man, 181 

113.  Horizontal  Section  of  a  Human  Pituitary  Body, 182 

114.  Acervulus  Cerebri  from  a  Human  Pineal  Body, .  183 

115.  Teased  Preparation  of  the  Gray  Substance  of  the  Wall  of  a  Ventricle  of  the  Human 

Brain, 183 

116.  Portion  of  the  Plexus  Choroideus  of  Adult  Man, 184 

117.  Cross-Section  of  Human  Median  Nerve, 186 

118.  Cross-Section  of  Human  Median  Nerve, 186 

119.  Longitudinal  Section  of  the  Spinal  Ganglion  of  a  Calf, 188 

1 20.  Cross-Section  of  the  Gasserian  Ganglion  of  Man, 189 

121.  Section  of  the  Superior  Cervical  Ganglion  of  Man, 189 

122.  Tactile  Corpuscle,  Cells  of  Langerhans,  Intra-Epithelial  Nerve-Fibers,  in  a  Section 

of  the  Skin  of  a  Human  Toe, 191 

123.  Tactile  Cells  in  a  Section  of  the  Skin  of  a  Human  Toe, 191 

124.  Compound  Tactile  Cells  from  the  Beak  of  a  Goose, 192 

125.  Cylindrical  End-Bulb  from  the  Conjunctiva  of  a  Calf, 193 

126.  Lamellar  Corpuscle  from  the  Mesentery  of  a  Cat, 193 

127.  Tactile  Corpuscle  from  a  Section  of  a  Human  Toe, 194 

128.  Motor  Nerve-Endings  of  the  Intercostal  Muscles  of  a  Rabbit 195 

129.  Motor  Nerve-Ending  in  an  Ocular  Muscle-Fiber  of  a  Rabbit, 196 

130.  Section  of  the  Suprarenal  Body  of  a  Child, 197 

131.  Section  through  Cortex  and  Medulla  of  the  Suprarenal  Body  of  Adult.Man,    ...  198 

132.  Section  of  Human  Cerebral  Cortex, 201 

133.  Transverse  Section  of  a  Peripheral  Spinal  Nerve, 203 

134.  Section  of  the  Mucous  Membrane  of  the  Lip  of  Adult  Man, 209 

135.  Longitudinal  Section  of  Human  Tooth, 210 

136.  Longitudinal  Section  of  a  Human  Molar  Tooth, 211 

137.  Longitudinal  Section  of  the  Fang  of  a  Human  Molar  Tooth, 211 

138.  Enamel  Prisms  from  the  Tooth  of  an  Infant, 212 

139.  Six  Odontoblasts  with  Dentinal  Fibers, 212 

140.  Schematic  Representation  of  the  Initial  Processes  in  the  Development  of  the  Teeth,  213 

141.  Frontal  Section  of  the  Head  of  an  Embryo  Sheep, 213 

142.  Section  of  the  Lower  Jaw  of  a  Human  Embryo  Four  Months  Old 214 

143.  Section  of  the  Upper  Jaw  of  a  Human  Embryo  Five  Months  Old, 215 

144.  Longitudinal  Section  of  a  Milk-Tooth  of  a  Newborn  Dog,     .    .    216 

145.  Longitudinal  Section  of  the  Mucous  Membrane   of  the    Dorsum   of  the  Human 

Tongue, 218 

146.  Longitudinal  Section  of  the  Mucous  Membrane  of  the  Human  Tongue, 218 

147.  Vertical  Section  of  a  Circumvallate  Papilla  of  Man, 219 

148.  Vertical  Section  of  a  Lymph-Follicle  from  the  Root  of  the  Tongue  of  Adult  Man,  .  219 


XVI  LIST    OF    ILLUSTRATIONS. 

FIG-  PAGE 

149.  Thin  Section  of  a  Lingual  Follicle  of  Man, 220 

150.  A  Serous  Gland  from  the  Tongue  of  a  Mouse, 221 

151.  Tubules  of  Human  Mucous  and  Serous  Glands, 222 

152.  Cross-Section  of  the  Middle  Third  of  the  Human  Esophagus, 224 

153.  Transverse  Section  of  a  Human  Stomach, 225 

154.  Vertical  Section  of  the  Cardial  End  of  a  Human  Stomach, 226 

155.  Tranverse  Section  of  a  Human  Fundus  Gland, .    227 

156.  Section  of  the  Mucous  Membrane  of  the  Fundus  of  the  Stomach  of  a  Mouse  (during 

Digestion), 227 

157.  Section  of  the  Human  Pyloric  Mucous  Membrane, 228 

158.  Section  of  the  Jejunum  of  Adult  Man, 230 

159.  Section  of  the  Mucous  Membrane  of  the  Jejunum  of  Adult  Man, 231 

160.  Section  of  the  Mucous  Membrane  of  the  Large  Intestine  of  Adult  Man, 231 

161.  Intestinal  Epithelium, 232 

162.  Longitudinal  Section  of  the  Apex  of  a  Villus  of  a  Dog, 233 

163.  Longitudinal  Section  through  the  Duodenum  of  a  Cat, 234 

164.  Transverse  Section  of  a  Patch  of  Peyer  of  the  Small  Intestine  of  a  Cat, 235 

165.  Crest  of  a  Solitary  Follicle  from  the  Small  Intestine  of  a  Kitten, 236 

166.  Section  of  the  Injected  Small  Intestine  of  a  Rabbit, 237 

167.  Plexus  Myentericus  and  Plexus  Submucosus  of  an  Infant, 239 

168.  Cross-Section  of  Human  Sublingual  Gland, 240 

169.  Section  of  Human  Parotid  Gland, 241 

170.  Section  of  Human  Submaxillary  Gland, 241 

171.  Gland-Cells  from  the  Pancreas  of  a  Cat ;   Section  of  the  Pancreas  of  an  Infant,  .    .    241 

172.  Transverse  Section   of  a   Gland-Tubule    of  the    Pancreas   of  Necturus,  showing 

Zymogen  Granules,    . 242 

173.  Section  of  Pancreas  of  Adult  Man, 242 

174.  Section  of  the  Submaxillary  Gland  of  a  Dog, 242 

175.  Scheme  of  an  Hepatic  Lobule,     ........  244 

176.  Liver-Cells  of  Man, 245 

177.  Horizontal  Section  of  Human  Liver, 245 

178.  Transverse  Section  of  the  Liver  of  a  Dog, 246 

179.  Bile-Capillaries  from  the  Liver  of  a  Dog, 247 

1 80.  Horizontal  Section  of  the  Injected  Liver  of  a  Rabbit, 248 

181.  Horizontal  Section  of  the  Injected  Liver  of  a  Cat, 248 

182.  Vertical  Section  of  the  Injected  Liver  of  a  Cat, 249 

183.  Section  of  the  Liver  of  a  Rabbit,  showing  Portal  Capillaries  and  Bile-Capillaries 

Injected,      249 

184.  Scheme  of  an  Ordinary  Gland-Tubule  and  of  an  Hepatic  Tubule, 250 

185.  Section  of  the  Liver  of  a  Rabbit,  with  Injected  Bile-Capillaries, 250 

1 86.  Shaken  Section  of  Human  Liver,        . 250 

187.  Scheme  of  a  System  of  Excretory  Channels, 252 

188.  Scheme  of  the  Liver, 252 

189.  Scheme  of  a  Transverse  Section  of  the  Liver, 253 

190.  Greater  Omentum  of  a  Rabbit,     .        254 

191.  Isolated  Fundus  Gland  of  a  Rabbit, 258 

192.  Intestinal  Villus  of  a  Rabbit, 259 

193.  Intestinal  Glands  of  a  Rabbit, 261 

194.  Section  of  a  Bronchus  of  a  Child, 268 

195.  Section  of  Lung  of  Adult  Man, 269 

196.  Sections  of    Human  Lung  and  of   the  Lung    of  a  Kitten,   showing   Respiratory 

Epithelium, 270 

197.  Section  of  Lung' of  a  Rabbit,  showing  Elastic  Fibers, 271 


LIST    OF    ILLUSTRATIONS.  XV11 

FIG.  PAGE 

198.  Section  of  Lung  of  a  Child,  Injected  through  the  Pulmonary  Artery, 271 

199.  Section  of  Thyroid  Gland  of  Adult  Man, 272 

200.  Section  of  the  Thymus  Body  of  a  Rabbit  Seven  Days  Old, 273 

201.  Corpuscle  of  Hassall, 274 

202.  Scheme  of  the  Course  of  the  Uriniferous  Tubules  and  of  the  Renal  Blood- Vessels,  .  278 

203.  Isolated  Uriniferous  Tubules  of  a  Rabbit, 278 

204.  Section  of  Human  Kidney, 279 

205.  Scheme  of  a  Renal  Corpuscle, 279 

206.  Section  of  Cortex  of  the  Kidney  of  a  Mouse,  showing  the  connection  between 

Bowman's  Capsule  and  the  Uriniferous  Tubule, 279 

207.  Isolated  Cell  of  a  Proximal  Convoluted  Tubule ;  Cross-Section  of  a  Proximal  Con- 

voluted Tubule, 280 

208.  Section  through  the  Cortex  of  a  Human  Kidney, 281 

209.  Transverse  Section  through  the  Medulla  of  a  Human  Kidney, 281 

210.  Longitudinal  Section  of  the  Injected  Kidney  of  a  Guinea-Pig, 282 

2H.     Nerve-Plexus  in  a  Section  of  the  Kidney  of  a  Mouse, 283 

212.  Transverse  Section  of  the  Lower  Half  of  a  Human  Ureter, 284 

213.  Vertical  Section  of  a  Human  Vesical  Mucous  Membrane, 284 

214.  Section  of  the  Testicle  of  a  Newborn  Child, 290 

215.  Section  of  the  Testicle  of  an  Ox, 290 

216.  Section  of  Seminiferous  Tubules  of  a  Mouse, < 291 

217.  Human  Spermatozoa,    ..."      293 

218.  Section  of  an  Adult  Human  Ductulus  Efferens  Testis, 294 

219.  Section  of  a  Human  Ductus  Epididymidis 295 

220.  Section  of  the  Initial  Portion  of  a  Human  Ductus  Deferens, 295 

221.  Section  of  the  Cavernous  Portion  of  the  Human  Urethra, 297 

222.  Section  of  the  Ovary  of  a  Child  Eight  Years  Old, 298 

223.  Section  of  an  Ovary  of  an  Infant  Four  Weeks  Old, 299 

224.  Section  of  the  Cortex  of  the  Ovary  of  a  Rabbit, 299 

225.  Section  of  a  large  Graafian  Follicle  of  a  Child  Eight  Years  Old, 300 

226.  An  Ovum  from  the  Graafian  Follicle  of  a  Cow, 301 

227.  Corpus  Luteum  of  a  Rabbit ;  Corpus  Luteum  of  a  Cat, 302 

228.  Section  of  the  Middle  of  the  Uterus  of  a  Girl  Fifteen  Years  Old,      304 

229.  Mucous  Membrane  of  the  Resting  Uterus  of  a  Young  Woman, 305 

230.  Mucous  Membrane  of  a  Virgin  Uterus  during  the  first  day  of  Menstruation,     .    .    .  307 

231.  Vertical  Section  through  the  Mucous  Membrane  of  a  Human  Uterus  One  Month 

Pregnant, .  308 

232.  Vertical  Section  through  the  Wall  of  a  Uterus  about  Seven  Months  Pregnant,  with 

the  Fetal  Membranes  in  situ, 309 

233.  Decidual  Cells, 310 

234.  Section  through  a  Normal  Human  Placenta  of  about  Seven  Months,  in  situ,   .    .    .  312 

235.  Diagram  of  Human  Placenta  at  the  close  of  Pregnancy,      .    .    .    .    » 313 

236.  Section  through  a  Smaller  and  Larger  Chorionic  Villus  of  a  Human  Placenta  at  the 

end  of  Pregnancy, 314 

237.  Isolated  Elements  of  the  Testicle  of  an  Ox, 318 

238.  Vertical  Section  of  the  Skin  of  the  Finger  of  Adult  Man, 322 

239.  Epidermis  from  the  Skin  of  the  Dorsum  of  the  Human  Foot, 322 

240.  Section  through  the  Skin  of  the  Sole  of  the  Foot  of  Adult  Man, 324 

241.  Cross-Section  of  the  Third  Phalanx  of  a  Child,    . 325 

242.  Elements  of  Human  Nail, 326 

243.  Cross-Section  of  Human  Scalp, 327 

244.  Elements  of  a  Human  Hair  and  Hair-Follicle,      328 

245.  Cross-Section  of  a  Hair  and  Hair- Follicle  in  the  Lower  Half  of  the  Root,    ....  329 


XV111  LIST    OF   ILLUSTRATIONS. 

FIG.  PAGE 

246.  Sections  of  the  Skin  of  an  Embryo  Four  Months  Old  and  of  an  Embryo  Five  and  a 

Half  Months  Old,  showing  the  Development  of  a  Hair  and  Hair  Follicle,  .    .    .  330 

247.  Vertical  Section  of  the  Hairy  Scalp  of  Adult  Man, 331 

248.  Vertical  Section  through  the  Ala  Nasi  of  a  Child, 332 

249.  Vertical  Section  of  the  Injected  Skin  of  the  Sole  of  a  Human  Foot,     ......  334 

250.  Section  of  the  Mammary  Gland  of  a  Pregnant  Rabbit,     .    .        335 

251.  Section  of  the  Mammary  Gland  of  a  Woman  last  Pregnant  two  years  before,       .    .  336 

252.  Human  Milk-Globules  ;   Elements  of  the  Colostrum  of  a  Pregnant  Woman,    .    .    .  337 

253.  Vertical  Section  of  a  Human  Cornea, 342 

254.  Corneal  Canaliculi  and  Corneal  Spaces, 343 

255.  Corneal  Corpuscles, 343 

256.  Section  through  the  Human  Sclera  and  Choroid, 343 

257.  Teased  Preparation  of  a  Human  Choroid, 344 

258.  Meridional  Section  through  the  Right  Iridocorneal  Angle  of  Man, 345 

259.  Vertical  Section  of  the  Pupillary  Portion  of  a  Human  Iris, 346 

260.  Vertical  Section  of  a  Human  Retina, 348 

261.  Vertical  Section  of  the  Retina  of  a  Rabbit, 349 

262.  Scheme  of  the  Elements  of  the  Retina,      351 

263.  Isolated  Elements  of  the  Retina  of  an  Ape, 353 

264.  Section  through  the  Macula  and  the  Center  of  the  Fovea, 354 

265.  Meridional  Section  of  the  Ora  Serrata  and  the  Adjacent  Portion  of  the  Pars  Ciliares 

Retinge  of  a  Man  Thirty-seven  Years  of  Age, 356 

266.  Section  of  the  Optic  Entrance  of  a  Human  Eye, 35 8 

267.  Lens-Fibers  of  an  Infant, 359 

268.  Capsule  and  Epithelium  of  an  Adult  Human  Lens, 359 

269.  Scheme  of  the  Vessels  of  the  Eye, 361 

270.  Vertical  Section  of  the  Human  Cornea,  showing  Nerve-Fibers, 364 

271.  Sagittal  Section  of  the  Upper  Eyelid  of  a  Child  Six  Months  Old, 366 

272.  Section  of  a  Human  Lacrymal  Gland, 369 

273.  Otoliths  from  the  Sacculus  of  an  Infant, 37& 

274.  Section  through  the  Second  Turn  of  the  Cochlea  of  an  Infant, 379 

275.  Surface  View  of  the  Lamina  Spiralis  of  a  Cat,      .    .  3^° 

276.  Surface  View  of  the  Lamina  Spiralis  Membranacea  of  a  Cat, 381 

277.  Lamina  Spiralis  of  a.  Cat  seen  from  the  Vestibular  Surface, 381 

278.  Scheme  of  the  Structure  of  the  Tympanic  Wall  of  the  Duct  of  the  Cochlea,  ...  382 

279.  Surface  View  of  the  Lamina  Spiralis  Membranacea  of  a  Cat, 383 

280.  Radial  Section  of  the  Peripheral  Half  of  the  Lamina  Spiralis  Ossea  and  the  Lamina 

Spiralis  Membranacea  of  an  Infant, 3^4 

281.  Scheme  of  the  Blood- Vessels  of  the  Right  Human  Labyrinth, 386 

282.  Scheme  of  the  Blood- Vessels  of  the  Right  Half  of  the  First  and  Second  Turns  of 

the  Cochlea, 387 

283.  Section  of  the  Skin  of  the  External  Auditory  Meatus  of  an  Infant, 389 

284.  Section  of  a  Coil-Tubule  of  the  External  Auditory  Meatus  of  an  Infant ;   Section  of 

a  Coil-Tubule  of  the  External  Auditory  Meatus  of  a  Twelve-Year-Old  Boy,  .    .  389 

285.  Section  of  the  Respiratory  Mucosa  of  the  Human  Nasal  Septum, 393 

286.  Isolated  Cells  of  the  Olfactory  Mucosa  of  a  Rabbit, 394 

287.  Vertical  Section  of  the  Olfactory  Region  of  a  Young  Rat, 395 

288.  Vertical  Section  of  the  Olfactory  Mucosa  of  a  Rabbit, 396 

289.  Vertical  Section  through  the  Olfactory  Mucosa  of  a  Rabbit, 39° 

290.  Vertical  Section  of  Two  Ridges  of  the  Papilla  Foliata  of  a  Rabbit, 399 

291.  Tastebud  of  the  Papilla  Foliata  of  a  Rabbit, 400 

292.  Nerves  of  the  Papilla  Foliata  of  a  Rabbit, 4°o 


PART  I. 

GENERAL  TECHNIC 


I.   THE   LABORATORY   APPOINTMENTS. 


i.  INSTRUMENTS. 

The  Microscope. — From  my  own  experience  I  can  recommend  the 
microscopes  made  in  the  optical  works  of  Leitz  in  Wetzlar,  Seibert  in 
Wetzlar,  and  Zeiss  in  Jena,  having  repeatedly  tested  their  excellent 
workmanship.* 

It  is  not  advisable  for  the  beginner  to  purchase  a  microscope 
without  first  submitting  it  to  an  expert  for  examination.  In  order 
to  preserve  the  microscope  in  good  working  condition  it  is  necessary  to 
protect  it  from  dust ;  when  in  frequent  use  it  is  best  to  keep  it  under  a 
bell-glass,  in  a  place  not  exposed  to  sunlight.  The  tarnish  which  forms 
on  the  tube  should  be  rubbed  off  with  a  dry  piece  of  soft  filter-paper. 

*  Students  of  the  first  semester  are  advised  to  refrain  from  the  purchase  of  high-power 
oculars  and  immersion- systems.  These  should  be  bought  shortly  before  entering  upon  bacterio- 
logical work. 

The  following  outfits  are  recommended  : 
Leitz. — Catalogue  No.  36,  1895.     Microscope  No.  4  b.       Price,  370  M.  =  $92.00.      Without 

homogeneous  immersion  and  ocular  IV,  265  M. 
Seibert. — Catalogue  No.   25,  1895.     Microscope  3   c.     Price,   449  M.  =  $112.00.      Without 

homogeneous  immersion,  objective  3,  and  ocular  o,  283.50  M.  —  $71.00. 
Zeiss. — Catalogue  No.   30,  1895.     Combination   (p.    116)    7  b.       Price,  602  M.  =    $150.00. 

Without  homogeneous  immersion,  442    M.  =    $ilo.oo;    or  8  b.     Price,   559  M.  = 

$140.00.     Without  homogeneous  immersion,  399  M.  =  $100.00. 

The  majority  of  the  work  for  this  book  was  carried  out  with  a  Leitz  microscope. 

Editor's  remark:  Of  American  microscopes  those  made  by  the  Bausch  &  Lomb 
Optical  Co.,  Rochester,  N.  Y.,  and  New  York  City,  are  recommended. 

For  histological  work  the  following  outfit  is  suitable : 

Stand  BB. — Oculars,  i-inch  and  3-inch.  Objectives,  %-inch  and  ^-inch.  Catalogue 
1895.  Price,  $62.50.  For  cytological  and  bacteriological  work  a  ^-inch  oil-immersion 
objective  (price,  $44)  and  an  Abbe  condenser  and  iris-diaphragm  should  be  added.  For 
convenience  a  double  or  triple  revolver  for  the  objectives  is  desirable. 


1 8  HISTOLOGY. 

Smirches  on  the  lenses  and  on  the  mirrors  should  be  removed  with  soft 
eather,  and  if  this  does  not  'answer  the  purpose — as,  for  example,  'when 
a  lens  is  smeared  with  Canada-balsam  or  damar-varnish — a  small  piece  of 
fine  linen  moistened  with  a  drop  of  pure  alcohol  should  be  used.  In 
the  latter  procedure  great  care  must  be  exercised  lest  the  alcohol  pene- 
trate the  setting  of  the  lenses  and  dissolve  the  balsam  with  which  they 
are  cemented  together.  Therefore  the  balsam  should  be  quickly  rubbed 
off  with  the  moistened  linen  and  the  lens  carefully  dried.  The  screws  of 
the  microscope  should  be  cleaned  with  benzin.  The  lenses  of  the  objec- 
tive must  not  be  unscrewed. 

A  good  razor,  flat  on  one  side.  It  should  always  be  kept  sharp, 
and  before  each  use  should  be  drawn  without  pressure  over  the  strop. 
The  honing  of  it  should  be  left  to  the  instrument-maker.  The  razor 
should  be  used  only  in  the  preparation  of  microscopic  sections. 

A  fine  whetstone. 

A  pair  of  fine,  straight  scissors. 

A  pair  of  easily-closing  fine  forceps,  with  smooth  or  only  slightly 
notched  points. 

Four  dissecting  needles  with  wooden  holders  :  two  are  to  be  heated, 
then  slightly  bent,  heated  again  and  thrust  into  solid  paraffin,  by  which 
they  are  again  hardened.  The  other  two  must  be  kept  clean  and  sharply 
pointed  ;  for  delicate  dissections  the  needles  must  be  pointed  and  polished 
first  on  the  whetstone  and  then  on  the  strop. 

A  flexible  section- lifter,  for  the  transfer  of  sections  from  fluids  to  the 
slide,  is  very  useful  but  not  absolutely  necessary.  A  scalpel  having  a 
broad  blade  can  be  used  instead. 

Pins,  quills,  cork  disks,  a  fine  sable  brush. 

A  crayon,  for  writing  on  glass.  If  the  glass  be  oily,  it  should  first 
be  cleansed  with  a  little  alcohol. 

Slides,  of  clear  glass  and  not  more  than  I  to  1.5  mm.  in  thickness. 

Cover-glasses.  Those  measuring  15  to  18  mm.  in  diameter  are 
generally  large  enough  ;  the  thickness  may  vary  from  o.  I  to  0.2  mm. 

Small  wide -mouthed  bottles.  One  dozen,  capacity  30  c.c.  and  over, 
with  cork  stoppers. 

Several  glass  preparation  jars  (preserve  jars),  with  tightly-fitting 
covers.  Height,  8  to  12  cm.;  diameter,  6  to  10  cm. 

A  cylindrical  graduate,  capacity  100  to  150  c.c. 

A  glass  funnel,  upper  diameter  8  to  10  cm. 

A  pipette.  Small  pipettes  may  be  prepared  by  heating  in  a  gas-flame 
a  glass  tube  I  cm.  thick  and  10  cm.  long,  pulling  one  end  to  a  point  and 
placing  on  the  other  a  small  rubber  bulb. 


THE    LABORATORY    APPOINTMENTS.  19 

A  dozen  watch-glasses  of  5  cm.  diameter. 

A  dozen  test-tubes  10  cm.  long  and  12  mm.  wide. 

Glass  rods  3  mm.  thick,  I  5  cm.  long,  some  drawn  to  a  point  at  the 
end. 

Old  bottles  that  have  been  thoroughly  cleansed  will  answer  as  recep- 
tacles for  reagents.  In  most  cases  the  bottles  can  be  cleansed  with  water, 
but  sometimes  it  is  necessary  to  rinse  them  with  crude  hydrochloric  acid 
or  with  potash  lye,  then  with  ordinary  water,  then  with  distilled  water, 
and  finally  with  alcohol. 

Glass  dishes  (Stender  dishes),  6  to  8  cm.  in  diameter,  with  ground 
covers,  are  not  absolutely  necessary,  but  very  useful.*  In  many  cases 
they  may  be  replaced  by  saucers,  food  dishes  for  birds,  etc. 

A  few  sheets  of  thin,  white  filter-paper,  large  and  small  gummed 
labels,  soft  pieces  of  linen  (old  handkerchiefs),  a  towel,  a  large  and  a 
small  bottle-brush. 

A  large  earthen  jar  for  refuse. 

2.  REAGENTS.f 

General  Rules. — Large  quantities  of  reagents  should  not  be  kept 
on  hand,  because  many  decompose  in  a  comparatively  short  time.  Cer- 
tain reagents  (see  below)  should  be  procured  or  prepared  shortly 
before  they  are  to  be  used.  Each  bottle  should  be  provided  with  a  large 
label  on  which  its  contents  are  designated  ;  it  is  advisable  to  write  on  the 
label  not  only  the  formula  of  the  reagent,  but  also  the  mode  of  its  appli- 
cation. All  the  bottles  must  be  tightly  closed  with  cork  or  good  glass 
stoppers.  The  fluid  should  not  reach  to  the  lower  surface  of  the  cork. 

1.  Distilled  water,  3  to  6  liters. 

2.  Normal  salt  solution,   0.75   per  cent,  (sodium  chlorid,  1.5   gm.; 
distilled  water,  200  c.c.). 

The  cork  must  be  provided  with  a  glass  rod  reaching  to  the  bottom 
of  the  bottle.  This  solution  spoils  easily  and  must  be  frequently  pre- 
pared afresh. 

3.  Alcohol,    (a)  Ninety-five  per  cent.  Alcohol. — About  500  c.c.  should 


*  Most  of  the  glassware,  including  slides  and  cover-glasses,  here  enumerated  may  be  ob- 
tained of  W.  P.  Stender,  Leipzig;  or,  in  the  United  States,  of  the  Bausch  &  Lomb  Optical 
Co.,  New  York. 

f  The  reagents  must  be  obtained  from  a  reputable  dealer.  Excellent  dyes  and  reagents 
may  be  had  of  Dr.  Griibler,  chemical  and  physiological  laboratory,  Leipzig,  Bayer'sche  Strasse  63. 
In  the  United  States  Griibler' s  stains  and  reagents  are  sold  by  Eimer  &  Amend,  New  York, 
and  others. 


2O  HISTOLOGY. 

be  kept  on  hand.  The  alcohol  of  commerce  is  95  per  cent.,  and  in  the 
majority  of  cases  is  entirely  satisfactory  for  microscopic  purposes.  If  it 
is  desired  to  obtain  alcohol  free  from  water  (absolute  alcohol),  drop  into 
the  bottle  a  few  pieces  of  copper  sulphate  heated  to  white  heat  (15  gm. 
to  100  c.c.  of  alcohol).  When  these  become  blue  they  must  be  replaced  by 
new  pieces  or  be  reheated.  Fresh  quicklime  serves  the  same  purpose, 
but  acts  more  slowly.* 

($)  Ninety  per  cent.  Alcohol. — Prepare  500  c.c.  by  diluting -47 5  c.c. 
of  95  per  cent,  alcohol  with  25  c.c.  of  distilled  water. 

(<r)  Seventy  per  cent.  Alcohol. — Prepare  500  c.c.  by  mixing  370  c.c. 
of  95  per  cent,  alcohol  with  130  c.c.  of  distilled  water. 

(d)  Fifty  per  cent.  Alcohol. — -Prepare  500  c.c.  by  mixing  265  c.c.  of 
95  per  cent,  alcohol  with  235  c.c.  of  distilled  water. 

(e)  Thirty-three  per   cent.  Alcohol  (Ranvier's  one-third  alcohol). — 
This  is  prepared  by  mixing  40  c.c.  of  95  per  cent,  alcohol  with  60  c.c. 
of  distilled  water. 

4.  Acetic  Acid,  59  c.c. — The  official  is  30  per  cent. 

5.  Glacial  Acetic  Acid. — This  should  be  procured  shortly  before  it  is 
required.     The  commercial  acid  is  96  per  cent. 

6.  Nitric  Acid. — A  bottle  holding   100  c.c.  of  concentrated  nitric 
acid  of  1. 1 8  sp.  gr.  (containing  32  per  cent,  of  acid  hydroxid)  should 
be  kept  in  stock. 

7.  Hydrochloric  acid,  pure,  50  c.c. 

8.  Chromic  Acid. — A  10  per  cent,  stock  solution  should  be  prepared 
by  dissolving    10  'gm.   of  fresh    crystalline   chromic  acid    in   90  c.c.   of 
distilled  water.      From  this  can  be  made  : 

(a)  A  o.i  per  cent,  chromic-acid  solution  (10  c.c.  of  stock  solution 
to  990  c.c.  of  distilled  water),  and — 

(b)  A  0.5  per  cent,  chromic-acid  solution  (50  c.c.  of  stock  solution 
to  950  c.c.  of  distilled  water). 

9.  Potassium   Bichromate. — This  should    be   kept  on  hand  in  two 
solutions  : 


*  For  the  preparation  of  mixtures  containing  a  smaller  percentage  of  alcohol  this  equation 

will  serve : 

loo  :  95  =  x  :  % 

e.g.,  90%,  loo  :  95  =  x  :  90 
95  x  =  90.   100 

oooo 
x  =  ^—  =  94.7  or  95. 

Therefore,  to  obtain  100  c.c.  of  90  per  cent,  alcohol,  95  c.c.  of  95  per  cent,  alcohol  must 
be  mixed  with  5  c.c.  of  distilled  water.  For  our  purposes  the  errors  of  this  ratio  are  too  insignifi- 
cant for  consideration. 


THE    LABORATORY    APPOINTMENTS.  21 

(«)   25  gm.  to  1000  c.c.  of  distilled  water. 

(fy  35  gm-  to  IO°°  c-c-  °f  distilled  water  (for  the  Golgi  mixture, 
No.  12). 

At  room  temperature  it  dissolves  in  from  three  to  six  days.  There- 
fore make  the  solutions  with  warm  water  or  place  the  bottles  near  the 
stove. 

10.  Midler  s  Fluid. — Dissolve  30  gm.  of  sodium  sulphate  and  60 
gm.  of  plilverized  potassium  bichromate  in  3000  c.c.  of  distilled  water. 
The  solution  can  be  made  with  the  aid  of  heat,  like  No.  9. 

11.  Zenker's  Fluid. — Dissolve  25  gm.  of  potassium  bichromate,  10 
gm.  of  sodium  sulphate,  and   50  gm.  of  mercuric  chlorid  in  1000  c.c.  of 
warm  distilled  water.     Before  using  add  I   c.c.  of  glacial  acetic  acid  to 
each  20  c.c.  of  the  mixture. 

12.  Golgi' s  Mixture  (osmio-bichromate  mixture).i-r-This  is  prepared 
by  pouring  together  54  c.c.  of  the  3.5  per  cent,  solution   of  potassium 
bichromate  (9  &)  and  6  c.c.  of  the  2  per  cent,  osmic-acid  solution  (No. 
19).      It  should  be  prepared  shortly  before  it  is  to  be  used. 

For  the  "  fixation  "  of  the  Golgi  preparations  the  following  solutions 
are  required  : 

13.  Stronger  Hydrocliinone  Developer. — This  consists  of  5   gm.  of 
hydrochinone,  40  gm.  of  sodium  sulphite,  75   gm.  of  potassium  carbo- 
nate, and  250  gm.  of  distilled  water.      From  this  prepare  a  dilution  by 
adding  20  c.c.  of  the  mixture  to  230  c.c.  of  distilled  water.     In  a  well- 
closed  bottle  in  a  dark  place  it  keeps  for  weeks.    The  yellowish  coloration 
which  appears  in  time  does  not  depreciate  it. 

14.  Sodium  Hyposulphite  (10  gm.  in  50  c.c.  of  distilled  water). — It 
dissolves  quickly  without  the  aid  of  heat. 

15.  Cox- Golgi  Mixture. — This  is  prepared  by  pouring  together  40 
c.c.  of  a  5  per  cent,  solution  of  potassium  bichromate,  40  c.c.  of  a  5  per 
cent,  solution  of  corrosive  sublimate,  32  c.c.  of  a  5  per  cent,  solution  of 
potassium  chromate,  and  88  c.c.  of  distilled  water.     This  mixture  may 
be  kept  in  stock. 

1 6.  Picric  Acid. — Keep  on  hand  50  gm.  of  the  crystals  and  500  c.c. 
of  a  saturated  aqueous  solution,  in  which  undissolved  crystals  in  a  stratum 
2  to  3  mm.  deep  must  always  lie  on  the  bottom  of  the  bottle.      It  dissolves 
readily. 

17.  Picrosulphuric  Acid  (Kleinenberg's  solution). — This  is  prepared 
by  adding  4  c.c.  of  pure  sulphuric  acid  to  200  c.c.  of  a  saturated  aqueous 
solution  of  picric  acid  ;  a  copious  precipitate  occurs.      In  about  one  hour 
filter  the  mixture  and  dilute  the  filtrate  with  600  c.c.  of  distilled  water. 
The  residue  on  the  filter  is  to  be  thrown  into  the  refuse  jar. 


22  HISTOLOGY. 

1 8.  Chromic- acetic  Acid. — To  50  c.c.  of  the  0.5  per  cent,  chromic 
acid  solution   (8  V)  add    50  c.c.  of  distilled  water   and  3   to    5   drops  of 
glacial  acetic  acid. 

19.  Osmic  Acid. — This  may  be  obtained  from  the  dealer — 50  c.c. 
of  a   2   per  cent,    solution — shortly   before    it    is    needed.       It  is   very 
expensive.      It  should  be  kept  in  the  dark  or  in  a  dark  glass  bottle,  and 
if  well-stoppered  can  be  preserved  many  months. 

20.  Chromic-acetic-osmic  Acid  (Flemming's  mixture). — Prepare  a  I 
per  cent,  chromic -acid  solution  (5  c.c.  of  the    10  per  cent,  solution  [No. 
8]  to  45  c.c.  of  distilled  water)  and  add  12  c.c.  of  2  per  cent,  osmic  acid 
and  3  c.c.  of  glacial  acetic  acid.     This   mixture  is   not  injured  by  light 
and  can  be  kept  in  stock.* 

21.  Platinum  Chlorid. — Prepare  a  10  percent,  stock  solution,  2  gm. 
dissolved  in  20  c.c.  of  distilled  water. 

22.  Platinum-acetic-osmic  Acid  Mixture. — Pour  into  60  c.c.  of  a  I  per 
cent,  solution  of  platinum  chlorid  (6  c.c.  of  stock  solution  and  54  c.c.  of 
distilled  water)  8  c.c.  of  2  per  cent,  osmic  acid  solution  and  4  c.c.  of  glacial 
acetic  acid. 

23.  Silver  Nitrate. — A  I  per  cent,  solution  (i  gm.  of  silver  nitrate  in 
IOO  c.c.  of  distilled  water)  should  be  procured  a  short  time  before  it  is 
to  be  used.      In  a  dark  place  or  in  a  dark  bottle  it  can  be  preserved  for  a 
long  time. 

24.  Gold  CJilorid. — A  solution  of  I  gm.  of  gold  chlorid  in  100  c.c. 
of  distilled  water  should  be  procured  shortly  before  it  is  to  be  used.      It 
must  be  kept  in  the  dark  or  in  a  dark  bottle.     For  gold-chlorid  staining 
it  is  necessary  to  have  the  following  : 

25.  Formic  acid,  50  c.c. 

26.  Concentrated  potash  lye  (35  per  cent.),  30  c.c.    The  bottle  must 
have  a  rubber  stopper  that  is  pierced  by  a  glass  rod.      It  should  be  pro- 
cured from  the  druggist. 

27.  Glycerol. — One  hundred  c.c.  of  pure  glycerol  are  to  be  kept  in 
stock;  also  a  solution  of  5   c.c.  of  pure  glycerol   in   25   c.c.  of  distilled 
water.      The  growth  of  fungi,  which  soon  takes  place   in  this   mixture, 
may  be  prevented  by  the  addition  of  a  small  piece  of  camphor,  or  thymol. 
The  cork  of  the  bottle  should  be  provided  with  a  glass  rod. 

28.  Bergamot  oil  (green),  20  c.c.     The  bottle  should  have  a  cork 
pierced  by  a  glass  rod.     The   much-used   cheaper   clove   oil  scents  the 
whole  laboratory  and  its  occupants. 


*  Tissues  fixed  in  old  Flemming's  fluid  often  stain  badly,  because  the  acetic  acid  has 
evaporated  ;  5  to  20  drops  of  acetic  acid  newly  added  to  the  solution  removes  this  defect. 


THE    LABORATORY    APPOINTMENTS.  23 

(a)  Xylol. — This  is  to  be  used  in  special  cases  instead  of  bergamot 
oil.  Xylol  clears  more  strongly,  and,  on  account  of  its  sensitiveness  in 
preparations  incompletely  dehydrated,  is  not  recommended  to  beginners. 

29.  Damar-varnish   (of  Dr.   Fr.   Schonfeld   &   Co.    in   Diisseldorf) 
may  be  purchased  in  small  bottles  containing  about  5.0  c.c.  from  dealers 
in  artists'  materials.      If  it  is  too  thick  it  may  be  diluted  with  pure  turpen- 
tine.     It  has  the  proper  consistence  when  the  drops  from  an  immersed 
glass  rod  fall  without  spinning  long   threads.      Damar  is  preferable  to 
Canada-balsam  (diluted  with  chloroform),  which  clears  too  vigorously 
and  renders  tissues  too  transparent,  but  has  the  disadvantage  of  drying 
more  slowly  than  balsam.     The  cork  of  the  bottle  should  be  provided 
with  a  glass  rod.* 

(a)  Xylol-balsain,  solution  of  Canada-balsam  in  xylol,  a  substitute 
for  damar- varnish. 

30.  Cover-glass  Cement. — Dilute  Venetian  turpentine  with  enough 
ether  to  make  an  easily-flowing  liquid  ;    then  filtered  warm  (in  a  heated 
funnel)  and  the  filtrate  inspissated  on  a  sand-bath.      The  proper  con- 
sistency   is   attained    when   a   drop  transferred    with  a   glass   rod   to   a 
slide  hardens  at  once  and  becomes  so  firm  that  it  cannot  be   indented 
with  the  finger-nail.      Because  of  the  danger  of  fire,  it  is  better  to  have 
the  cement  prepared  by  the  druggist,  f 

31.  Hanseiis     Hematoxylin. — (a)  Dissolve    I    gm.   of   crystallized 
hematoxylin   in  10  c.c.  of  absolute  alcohol   and   preserve   it  in   a  stop- 
pered  bottle.      (U)    Dissolve    20   gm.    of   potassium    alum    in    distilled 
water,  with  the  aid  of  heat,  and  when  cold  filter,      (c)  Dissolve  I  gm.  of 
potassium  permanganate  in   16  c.c.  of  distilled  water,  at  room-tempera- 
ture.    On  the  next  day  pour  solutions  a  and  b  into  a  porcelain  capsule, 
add  3  c.c.  of  solution   c,  and,  with   constant  stirring,  heat  the   mixture 
to  boiling  and  Jx>il  about  one  minute.      Cool  quickly  by  floating  the  por- 
celain capsule  in  cold  water.     When  cold  the  mixture  should  be  filtered  ; 
it  is  then  ready  to  use.     Cloudiness,  or  the  development  of  fungi  in  the 
mixture,  does  not  depreciate  its  effectiveness  in  the  slightest  degree.      It 
is  to  be  kept  on  hand. 

32.  Delafield's  Hematoxylin. — (a)  Dissolve    I    gm.   of   crystallized 
hematoxylin    in   6  c.c.   of   absolute   alcohol.      (&)  Dissolve    1 5    gm.    of 
ammonia   alum  in    100  c.c.  of  distilled  water,  with  the  aid  of  heat,  and 
when  cold  filter.      Pour  the  two  solutions  together  and  let  the  mixture 

*  Editor's  remark :  Instead  of  this  commercial  damar-varnish  I  recommend  a  solution 
of  pure  gum  damar  in  xylol,  which  has  the  advantage  of  drying  more  quickly. 

f  Editor's  remark  :  In  the  United  States  an  excellent  fluid  cover-glass  cement  is  pre- 
pared by  J.  D.  King,  Cottage  City,  Mass. 


24  HISTOLOGY. 

stand  three  days  in  a  wide-open  vessel  exposed  to  the  light ;  then  filter 
and  mix  with  25  c.c.  of  pure  glycerol  and  25  c.c.  of  methyl-alcohol. 
After  three  days  filter  the  mixture.  It  does  not  deteriorate  with  age 
and  should  be  kept  in  stock. 

33.  Weigerf  s  Jiernatoxylin,  for  the  demonstration  of  the  medullated 
nerve-fibers  of  the  brain  and  the  spinal  cord.      Heat  I  gm.  of  crystallized 
hematoxylin  in  10  c.c.  of  absolute  alcohol  plus  90  c.c.  of  distilled  water, 
and  when  cold  filter.      It  should  be  prepared  shortly  before   it   is   to  be 
used.     The   application  of  this  stain  demands   the  aid  of  the  following 
three  fluids  : 

34.  Saturated    Solution  of  Lithium    Carbonate. — Dissolve    3   or    4 
gm.  of  lithium  carbonate  in  100  c.c.  of  distilled  water.     This  should  be 
prepared  the  day  before  using. 

35.  Solution  of  Potassium  Permanganate  (0.25  per  cent.). — Dissolve 
0.5  gm.  of  potassium  permanganate  in  200  c.c.  of  distilled  water.     This 
is  to  be  kept  on  hand. 

36.  Acid  Mixture  (Pal's  mixture). — Dissolve  I  gm.  of  pure  oxalic 
acid   and  I  gm.  of  potassium   sulphite  (K2SO3)  in    200   c.c.  of  distilled 
water.     This  mixture  should  be  prepared  one  day  before  using  and  kept 
in  a  well-stoppered  bottle. 

37.  Neutral  Carmine-solution. — Dissolve  I  gm.  of  the  best  carmine 
in  50  c.c.  of  cold  distilled  water  to  which  5  c.c.  of  a  solution  of  ammonia, 
sp.  gr.  0.960  (liquor  ammonii   caustici)  have  been  added.     The  deep, 
cherry-red  fluid  should  stand  in  an  open  vessel  until  it  has   no   odor  of 
ammonia  (about   three  days)  and  then   be  filtered.      It  is  to  be   kept  in 
stock.      The  odor  of  this  solution  immediately  becomes  very  disagree- 
able, but  this  does  not  depreciate  its  staining  power. 

38.  Picrocarminc. — Pour  5  c.c.  of  solution  of  ammonia  into  50  c.c. 
of  distilled  water,  and  to  this  mixture  add    I   gm.  of  the.  best  carmine. 
Stir  with  a  glass  rod.      After  complete  solution  of  the  carmine  (in  about 
five  minutes)  add  50  c.c.  of  a  saturated  solution  of  picric  acid  and  let  the 
whole  stand  in  a  wide-open  vessel  for  two  days.     It  is  then  to  be  filtered. 
Abundant  fungous  growth  does  not  diminish  the  staining  power  of  this 
excellent  medium. 

39.  Alum-carmine. — Dissolve   5   gm.  of  alum  in   100  c.c.  of  warm 
distilled   water   and  add   2   gm.  of  carmine.     Boil  this   mixture   ten  or 
twenty  minutes  and  when    cold   filter  ;   finally,  to   the   clear,  beautiful, 
ruby-red  fluid  add  2  to  3  drops  of  liquefied  carbolic  acid. 

40.  Borax-carmine. — Dissolve  4  gm.  of  borax  in  TOO  c.c.  of  warm 
distilled  water  ;  when  the  solution  has  cooled  add  3  gm.  of  the  best  car- 
mine, stirring  meanwhile,  and  then  100  c.c.  of  70  per  cent,  alcohol.     At 


THE    LABORATORY    APPOINTMENTS.  2  5 

the  expiration  of  twenty-four  hours  the  fluid  should  be  filtered.  It  filters 
very  slowly,  requiring  twenty-four  hours  or  more. 

Staining  with  borax-carmine  requires  after-treatment  with  70  per 
cent,  acid-alcohol,  which  is  prepared  by  adding  4  or  6  drops  of  pure 
hydrochloric  acid  to  100  c.c.  of  70  per  cent,  alcohol. 

Borax-carmine  and  acid-alcohol  should  be  kept  on  hand. 

41.  Sodium  Carminate. — Dissolve  2  gm.  of  the  pigment  in  200  c.c. 
of  distilled  water.* 

42.  Safranin. —  Dissolve  2  gm.   of  pigment  in  60  c.c.   of   50  per 
cent,  alcohol  (32  c.c.  of  95  per  cent,  alcohol  in  28  c.c.  of  distilled  water). 
It  is  to  be  kept  in  stock. 

43.  Eosin. — Dissolve  I  gm.  of  pigment  in  60  c.c.   of  50  per  cent, 
alcohol.     This  should  be  kept  in  stock. 

44.  Congo-red. — Dissolve  I  gm.  of  pigment  in  100  c.c.  of  distilled 
water.      From  this  stock-solution  prepare — 

(a)  A  3^  per  cent,  solution  :  3  c.c.  of  stock-solution  in  100  c.c.  of 
distilled  water. 

45.  Vesuvin,  or — 

46.  Methyl-violet  B.  may  be  kept  in   stock   in  a  saturated  aqueous 
solution  (i  gm.  in  50  c.c.  distilled  water). 

47.  Metliylene-blue. — Dissolve  I  gm.  in  100  c.c.    of  distilled  water. 
This  solution  keeps  well,  as  does  the  following,  which  is   required  for 
after-treatment. 

48.  Ammonium  Picrate. — Dissolve    3  gm.    in    100  c.c.   of  distilled 
water. 

49.  Orccin. — Dissolve  I  gm.  of  the  pigment  in  100  c.c.  of  absolute 
alcohol  and  add  I  c.c.  of  pure  hydrochloric  acid. 

50.  Wcstpliar s  Alum-carmine  Dahlia. — Dissolve  I  gm.  of  dahlia  in 
25  c.c.  of  absolute  alcohol,  add  12  c.c.   of  pure  glycerol  and    5   c.c.   of 
glacial  acetic  acid,  and  pour  into  this  mixture   25   c.c.  of  alum-carmine 
(No.  39,  p.  24).     Preserve  in  a  well-stoppered  bottle. 


*  Editor's  remark  :  Of  the  carmine  stains  alum-cochineal  deserves  to  be  highly  recom- 
mended. Because  of  its  certainty  and  of  the  simplicity  of  its  application  it  is  very  useful  in 
the  hands  of  the  beginner.  It  is  prepared  by  boiling  60  gm.  of  powdered  cochineal  and  60  gm. 
of  alum  in  800  parts  of  water  for  about  twenty  minutes,  filtering  the  decoction,  and  adding  a 
small  piece  of  camphor  or  thymol  to  prevent  the  growth  of  mold.  It  can  be  kept  in  stock 
for  a  long  time. 


II.    THE  PREPARATION  OF   MICROSCOPIC 
SPECIMENS. 

INTRODUCTION. 

Very  few  organs  of  the  animal  body  are  of  a  structure  suitable 
for  microscopic  examination  without  special  preparation.  They  must 
possess  a  certain  degree  of  transparency,  which  is  attained  either  by 
separating  the  organs  into  their  elements  or  by  cutting  them  into  thin 
sections, — that  is,  either  by  isolating  or  by  sectioning.  Further,  very 
few  organs  possess  a  consistency  that,  without  treatment,  allows  of  the 
cutting  of  sufficiently  thin  sections  ;  they  are  either  too  soft,  in  which 
case  they  must  be  hardened,  or  too  hard  (calcified),  in  which  case  they 
must  be  decalcified.  But  fresh  objects  can  be  neither  liardened  nor 
decalcified  without  injury  to  their  structure  ;  both  processes  must  be  pre- 
ceded by  treatment  which  kills  the  structural  elements  rapidly  and  at  the 
same  time  preserves  their  natural  form.  This  procedure  is  called  fixation. 
Usually,  the  preparation  of  thin  sections  is  possible  only  after  fixation  and 
hardening,  followed  in  some  cases  by  decalcification,  of  the  object.  The 
sections,  too,  require  further  treatment ;  they  may  be  forthwith  ren- 
dered transparent  by  means  of  clearing  media  (which  can  be  also  suc- 
cessfully applied  in  the  examination  of  fresh  objects),  or  they  may  be 
stainedbefore  being  made  transparent.  The  staining  materials  are  invalu- 
able agents  in  microscopic  investigations.  They  can  be  applied  in  the 
examination  of  fresh  and  even  of  living  organs.  Many  of  the  most 
important  facts  have  been  discovered  by  means  of  them.  Introduced 
into  the  blood-vessels,  injected,  they  enable  us  to  trace  the  branching  and 
course  of  the  finest  ramifications. 

§  i.    NATURE  OF  THE  MATERIAL. 

For  the  study  of  the  structural  elements  and  the  simplest  tissues, 
amphibians  (frogs,  salamanders)  are  recommended.  The  best  is  the 
spotted  salamander,*  the  elements  of  which  are  very  large.  For  the 

*  Editor's  remark  :    Or  the  American  Aniblystoma,  Necturus,  etc. 
26 


THE    PREPARATION    OF    MICROSCOPIC    SPECIMENS.  2/. 

study  of  organs,  mammals  should  be  chosen.  In  many  cases  our 
rodents  (rabbits,  guinea-pigs,  rats,  mice),  also  young  dogs,  cats,  etc., 
are  suitable.  Still,  no  opportunity  to  secure  human  organs  should 
be  neglected.  Perfectly  fresh  material  can  often  be  obtained  at  sur- 
gical clinics.  Material  may  also  be  had  at  autopsies,  if  not  made  too 
long  after  death  ;  with  the  exception  of  the  mucous  membrane  of  the 
intestinal  tract,  which  decomposes  very  quickly  after  death,  many  organs 
can  be  used. 

In  general  it  is  advisable  to  place  the  organs  while  yet  warm  in  the 
fixing  fluid.  In  order  to  accomplish  this  the  following  injunctions  must 
be  observed  :  Fill  the  bottles  selected  for  the  reception  of  the  objects 
with  the  appropriate  fluid  and  provide  them  with  a  label  on  which  is 
designated  the  object,  the  fluid,  the  date,  and  in  some  cases  the  hour  ; 
then  place  the  dissecting  instruments  near  at  hand  ;  then  kill  the  animal.* 


§  2.  KILLING  AND  DISSECTING  THE  ANIMALS. 

In  the  case  of  amphibians,  cut  through  the  vertebral  column  of  the 
neck  with  strong  scissors,  and  destroy  brain  and  spinal  cord  by  means 
of  a  nee'dle  introduced  through  the  wound  into  the  spinal  canal  and  the 
cranial  cavity.  In  the  case  of  mammals,  cut  the  throat  by  a  deep  incision 
reaching  as  far  back  as  the  vertebral  column,  or  pour  chloroform  on  a 
cloth  and  press  it  to  the  nose  of  the  animal,  f  Small  animals,  up  to  the 
size  of  four  centimeters,  and  embryos  may  be  placed  entire  in  the  fixing 
fluid  ;  after  about  six  hours  the  thoracic  and  abdominal  cavities  should 
be  opened  by  incisions.  In  the  dissection,  if  possible,  an  assistant  should 
hold  the  extremities  of  the  animal.  Small  animals  can  be  extended  on 
cork  or  wax  plates  and  secured  by  strong  pins  thrust  through  the  feet. 
The  organs  must  be  carefully  removed.  This  is  best  done  with  scissors 
and  forceps.  Crushing  or  pressing  the  parts,  or  taking  hold  of  them  with 
the  fingers,  must  be  entirely  avoided.  Only  the  edge  of  the  object  may 
be  grasped  by  the  forceps.  Attached  foreign  matter — mucus,  blood, 
contents  of  the  intestines — must  not  be  scraped  off  with  the  scalpel,  but 
should  be  removed  by  slow  twirling  in  the  respective  fixing  fluids. 

In  the  following  methods  it  is  not  possible  to  avoid  moistening  scis- 
sors, forceps,  needles,  glass-rods,  etc.,  with  different  fluids, — for  example, 


*  To  take  parts  from  the  living  animal  is  an  entirely  needless  cruelty  ! 

f  Editors  remark  :  I  prefer  to  kill  medium-sized  and  smaller  animals  (rabbits,  guinea- 
pigs,  cats,  mice,  etc.)  by  placing  them  under  a  sufficiently  large  bell-glass,  together  with  a  wad 
of  absorbent  cotton  saturated  with  chloroform. 


28  HISTOLOGY. 

with  acids.  The  instruments  should  therefore  be  cleaned  immediately 
after  using  by  rinsing  in  water  and  drying.  Above  all,  avoid  dipping  a 
glass-rod  which,  for  instance,  maybe  contaminated  with  an  acid  or  a  dye 
into  another  fluid.  Apart  from  the  fact  that  thereby  the  reagents  will 
be  spoiled,  the  success  of  the  preparation  is,  as  a  consequence,  often 
totally  frustrated.  Beaker-glasses,  watch-glasses,  etc.,  are  easy  to  clean 
if  attended  to  immediately  after  using  ;  but  if,  for  example,  any  staining 
fluid  is  allowed  to  evaporate  and  dry  on  them  the  cleansing  then  becomes 
very  tedious.  Therefore  the  cleansing  of  the  glasses  immediately  after 
using  should  never  be  neglected  ;  in  case  there  be  no  time  for  this,  they 
at  least  should  be  placed  in  water. 

All  vessels  used  for  isolating,  fixing,  hardening,  staining,  etc.,  must 
be  kept  closed,  and  should  not  be  placed  in  the  sun. 


§  3.    ISOLATING. 

The  process  of  isolation  is  accomplished  by  teasing  either  the  fresh 
objects  or  those  previously  treated  with  dissociating  fluids,  which  render 
the  teasing  partially  or  wholly  unnecessary.  It  is  a  difficult  task  to 
make  a  well-teased  preparation.  Great  patience  and  exact  fulfilment  of 
the  following  directions  are  indispensable  :  The  needles  must  be  sharp 
and  perfectly  clean  ;  they  should  be  previously  pointed  and  polished  on 
a  moistened  whetstone.  The  minute  object,  at  the  most  5  mm.  in 
length,  should  be  placed  in  a  small  drop  of  the  dissociating  or  mount- 
ing medium  on  a  slide  and  teased, — on  a  dark  background  if  it  is  color- 
less, on  a  white  surface  if  it  is  dark  or  colored.  If  the  tissue  is  fibrous — 
for  example,  a  bundle  of  muscle-fibers — apply  both  needles  at  one  end 
and  separate  the  fasciculus  along  its  length  into  two  ;  in  the  same  way 
divide  one  of  these  bundles  into  two,  and  so  continue  until  minute  individ- 
ual fibers  are  isolated.  At  times  it  is  difficult  to  divide  the  bundle  along 
its  entire  length  ;  in  this  case  it  is  often  sufficient  to  divide  it  for  three- 
fourths  of  its  length,  allowing  the  isolated  fibers  to  remain  attached  at 
the  one  end.  The  uncovered  preparation  may  be  examined  with  the 
low  power  in  order  to  ascertain  if  the  dissection  is  fine  enough.* 

The  following  isolating  fluids  are  recommended  : 

For  Epithelium. — Ranvier's  one-third  alcohol  (p.  20)  is  an  admirable 
dissociating  medium.  Place  small  pieces  from  5  to  10  mm.  in  length 


*  Uncovered  preparations  lying  in  a  small  amount  of  fluid  often  appear  indistinct,  exhibit 
black  borders,  etc.,  errors  which  may  be  corrected  by  the  addition  of  a  sufficiently  large  drop 
of  fluid  and  the  application  of  a  cover-glass. 


THE    PREPARATION    OF    MICROSCOPIC    SPECIMENS.  2Q 

(i\  £'.,  of  the  intestinal  mucous  membrane)  in  about  10  c.c.  of  this  fluid. 
After  four  hours  (in  the  case  of  stratified  squamous  epithelium  after  ten 
to  twenty-four  hours  or  later)  take  out  the  pieces  with  the  forceps,  care- 
fully and  slowly,  and  tap  them  lightly  against  a  slide  upon  which  a  drop 
of  the  same  fluid  has  been  placed.  By  this  manipulation  many  isolated 
epithelial-cells  fall  off;  occasionally  shreds  are  detached,  which  can  be 
separated  into  their  elements  by  teasing  them.  Then  apply  a  cover- 
glass  (p.  44)  and  examine.  If  it  is  desired  to  stain  the  object,  carefully 
transfer  the  entire  piece  from  the  alcohol  to  about  6  c.c.  of  picrocarmine 
(p.  24).  In  two  or  four  hours  place  the  object  very  carefully  in  5  c.c.  of 
distilled  water,  and  in  five  minutes  tap  it  against  the  slide,  which  this 
time  should  have  on  it  a  drop  of  diluted  glycerol  (p.  22).  Apply  a 
cover-glass.  The  preparation  can  be  preserved. 

For  Muscle-fibers  and  Glands. — A  35  per  cent,  solution  of  potassium 
hydroxid  is  suitable.  Small  cubes  from  10  to  20  mm.  in  diameter  should 
be  placed  in  10  to  20  c.c.  of  this  fluid.  In  about  an  hour  the  objects  fall 
apart  into  their  elements,  which  may  then  be  lifted  out  with  a  needle  or  a 
pipet  and  examined  under  a  cover-glass  in  a  drop  of  the  same  lye.  The 
action  of  diluted  potash  lye  is  totally  different  ;  examined  in  a  drop  of 
water  the  elements  are  rapidly  destroyed.  If  the  isolation  is  not  suc- 
cessful, and  instead  a  jelly-like  softening  occurs,  the  potash  solution  is 
too  old.  Therefore  a  freshly-prepared  solution  should  always  be  used. 
The  preparations,  even  when  successful,  cannot  be  preserved.* 

A  mixture  of  potassium  chlorate  and  nitric  acid  may  be  used.  This 
is  prepared  by  throwing  into  20  c.c.  of  pure  nitric  acid  enough  potassium 
chlorate  (about  5  gm.)  so  that  an  undissolved  residue  will  remain  on  the 
bottom  of  the  bottle.  In  from  one  to  six  hours,  occasionally  later,  the 
object  is  sufficiently  dissociated,  and  should  then  be  transferred  to  dis- 
tilled water,  in  which  it  should  stay  for  one  hour,  but  may  remain  for  a 
week  without  injury.  Then  the  object  is  placed  on  a  slide,  where,  in  a 
drop  of  diluted  glycerol  (p.  22),  it  can  be  easily  dissected.  If  the  nitric 
acid  is  well  washed  out  the  preparation  can  be  preserved  and  can  also  be 
stained  under  the  cover-glass  (p.  48).  Placing  the  unteased  objects  in 

*  Editor's  remark:  According  to  S.  H.  Gage  ("  Proc.  Amer.  Soc.  Micr.,"  1889,  p.  36), 
the  action  of  the  caustic  potash  may  be  at  any  time  most  satisfactorily  checked  by  replacing  it 
with  a  60  per  cent,  solution  of  potassium  acetate,  or  by  the  addition  of  sufficient  glacial  acetic 
acid  to  neutralize  the  caustic  potash  and  form  acetate  of  potash.  After  the  action  of  the  caustic 
potash  is  checked  the  elements  may  be  preserved  indefinitely  en  masse  in  a  60  per  cent,  solu- 
tion of  acetate  of  potash,  or  after  being  treated  with  a  saturated  solution  of  alum,  in  40  percent, 
alcohol  or  glycerol.  After  the  last  treatment  the  elements  may  even  be  satisfactorily  stained 
with  hematoxylin  or  alum-carmine. 


3O  HISTOLOGY. 

picrocarmine  (see  For.  Epithelium)  will  not  be   successful,  because  this 
staining  fluid  renders  them  brittle. 

For  gland-tubules  pure  hydrochloric  acid  is  excellent.  Small  pieces 
about  I  cm.  in  diameter  should  be  placed  in  loc.c.  of  the  acid  and  in  from 
ten  to  twenty  hours  transferred  to  about  30  c.c.  of  distilled  water,  which 
must  be  renewed  several  times  during  twenty-four  hours.  The  isolation 
is  then  easily  accomplished  by  carefully  spreading  out  the  pieces  with 
needles  in  a  drop  of  diluted  glycerol.  The  preparation  can  be  pre- 
served. 

§  4.   FIXATION. 

General  Rules. — (i)  For  fixation  a  large  quantity  of  the  fluid 
should  be  used,  exceeding  the  volume  of  the  object  50  to  100  times. 
(2)  The  fluid  must  always  be  clear,  and  so  soon  as  it  becomes  turbid  must 
be  replaced  by  fresh  fluid.  It  often  becomes  turbid  within  an  hour 
after  the  introduction  of  the  object.  (3)  The  objects  to  be  fixed  should 
be  as  small  as  possible  ;  in  general  they  should  not  exceed  I  or  2  c.c. 
Should  it  be  necessary  to  preserve  the  object  entire  (e.  g.,  for  subsequent 
orientation)  many  deep  incisions  should  be  made  in  it  from  five  to  ten 
hours  after  placing  it  in  the  fixation  medium.  The  object  should  not  lie 
on  the  bottom  of  the  receptacle,  but  should  be  suspended  within  it  or 
placed  upon  a  thin  layer  of  cotton-  or  glass-wool. 

1.  Ninety-five  percent,  alcohol  is  especially  suitable  for  fixing  glands, 
skin,  blood-vessels,  etc.      It  acts  simultaneously  as  a  hardening  medium. 
Objects  fixed  in  alcohol  can  be  sectioned  after  twenty-four  hours.*  There- 
fore it  is  well  adapted  for  the  rapid  preparation  of  specimens.      Special 
attention  should  be  given  to  the  following  details  :  (i)  The  alcohol  must 
be  renewed   in  from   three  to   four  hours,  even  though  it  is  not  turbid. 
(2)  The  objects  should  not  lie  in  contact  with  the  glass,  lest  they  adhere  to 
it ;  f  therefore  they  should  be  either  suspended  on  a  thread  in  the  alco- 
hol or  placed  on  a  little  wad  of  cotton  on  the  bottom  of  the  vessel. 

Weaker  alcohol — for  example,  90  per  cent,  alcohol — acts  very 
differently,  shriveling  the  object,  and  therefore  cannot  be  used  instead  of 
95  per  cent,  alcohol. 

2.  Chromic  acid  is  mainly  used  in  two  aqueous  solutions  : 


*  One  should  not  too  long  delay  using  objects  fixed  in  absolute  alcohol,  for  the  elements 
gradually  deteriorate  ;  they  should  be  sectioned  in  from  three  to  eight  days.  Sections  of  objects 
that  have  lain  only  twenty-four  hours  in  absolute  alcohol  occasionally  stain  poorly. 

f  Such  areas  appear  strongly  compressed  in  the  sections. 


THE    PREPARATION    OF    MICROSCOPIC    SPECIMENS.  3! 

(a)  As  a  o.  I  or  a  0.5  per  cent,  solution  (p.  20),  which  is  especially 
suitable  for  organs  that  contain  much  loose  connective  tissue.  This 
strong  solution  imparts  a  superior  consistence  to  connective  tissue,  but 
has  the  disadvantage  of  making  the  staining  difficult ;  it  is  also  suitable 
for  the  fixation  of  karyokinetic  figures.  The  objects  remain  in  the  chro- 
mic-acid solution  for  from  one  to  eight  days,  are  then  washed  in  running 
water  for  from  three  to  four  hours,  or,  if  this  is  not  possible,  placed  for  the 
same  length  of  time  in  water  renewed  three  or  four  times,  then  transferred 
to  distilled  water  for  a  few  minutes,  and  finally  hardened  in  alcohol  of 
gradually  increased  strength  (§  5)  and  protected  from  daylight  (p.  33, 
remark  *). 

(/;)  As  a  0.05  per  cent,  solution,  which  may  be  prepared  by  dilut- 
ing the  o.  I  per  cent,  solution  with  an  equal  volume  of  distilled  water. 
The  application  is  the  same  as  that  of  solution  a,  except  that  the  objects 
remain  only  twenty-four  hours  in  solution  b. 

Chromic-acid  solutions  penetrate  slowly  ;  accordingly,  if  the  tissue 
is  submitted  to  the  action  of  the  medium  for  so  brief  a  period  as  twenty- 
four  hours,  only  small  pieces,  5  to  10  mm.  in  diameter,  should  be  pre- 
served. 

3.  Nitric  acid  in  a   3    per   cent,   solution   (3    c.c.    of  concentrated 
nitric  acid  [p.  20]  to  97  c.c.  of  distilled  water),  like  the  strong  chromic- 
acid  solution,  is  an  admirable  medium  for  organs  rich  in  connective  tissue. 
The  objects  remain  for  from  five  to  eight  hours  in  this  solution  and  with- 
out the  previous  use  of  water  are  transferred    directly  into  alcohol  of 
gradually  increased  strength  for  hardening  (§  5). 

4.  Klcinenberg' s  Fluid  (p.  21). — Delicate  objects  (embryos)  should 
be  allowed  to  remain  in  this  fluid  for  five  hours,  more  solid  parts  for  from 
twelve  to  twenty  hours  ;  then,  without  previous  washing  in  water,  they 
are  hardened  in  alcohols  of  gradually  increased  strength  (§  5). 

5.  Midler  s  Fluid. — The  objects  remain  for  from  one  to  six  weeks  * 
in  a  large  volume  (up  to  400  c.c.)  of  this  solution,  are   then  washed   in 
(if  possible)  running  water,  rinsed   in   distilled   water,  and,  finally,  hard- 
ened in  the  series  of  gradually  ascending  alcohols,  under  exclusion  from 
daylight  (p.  33,  remark  *).     Who  does  not  follow  with  painstaking  con- 
scientiousness  the  above-specified   general  rules  for  fixation  will   secure 
imperfect  results,  for  which   even   otherwise  experienced   microscopists 
have  held  the  blameless  Miiller's  fluid  responsible. 

6.  Zcnkcrs  Fluid. — Metallic  instruments  must  be  cleansed  imme- 


*  Objects  may  be  left  in  Miiller's  fluid  for  a  longer  period — up  to  six  months  ;  often  they 
can  then  be  sectioned  and  stained  without  the  alcohol  hardening. 


32  HISTOLOGY. 

diately  after  dipping  them  into  this  fluid.  The  objects  should  remain  in 
it  for  from  twenty-four  to  forty-eight  hours,  allowing  about  60  c.c.  of  the 
reagent  to  each  one-centimeter  cube  of  tissue,  should  be  washed  in 
running  water  for  the  same  length  of  time,  rinsed  in  distilled  water,  and 
hardened  in  the  dark  in  alcohols  of  gradually  increasing  strength  (p.  33). 
For  the  removal  of  the  sublimate  precipitates  that  occur  in  the  tissues 
add  to  the  90  per  cent,  alcohol  enough  tincture  of  iodin  to  impart  to  the 
fluid  the  color  of  port-wine.  The  objects  remain  for  from  eight  to  fourteen 
days  in  this  iodin-alcohol,  the  color  of  which  rapidly  fades,  and  there- 
fore it  requires  the  daily  addition  of  enough  of  the  tincture  of  iodin  to 
maintain  the  desired  color.*  Finally  the  objects  are  transferred  to  pure 
90  per  cent,  alcohol,  which  is  to  be  changed  two  or  three  times,  and  in 
tliis  they  may  remain  for  a  week  or  longer.  (See  also  p.  47.) 

7.  Osmic-acid  Sohition  (p.  22). — In  using  this  reagent  care  must  be 
taken  not  to  inhale  the  vapor,  which  is  very  irritating  to  mucous  mem- 
branes.     Fixation  is  accomplished  either  by  immersing  very  small  pieces, 
up  to  5  mm.  cubes,  in  the  acid,  which  is  usually  employed  in  a  one  per 
cent,  solution,  of  which  only  a  small  quantity — from    I  to  6  c.c. — need 
be  used  ;  or  by  exposing  the  moist  object  to  the  vapor  of  the  osmic-acid 
solution.      For  the  latter  purpose  pour  I  c.c.  of  the  2  per  cent,  solution 
into  a  test-tube  about  5  cm.  in  length  and  add  an  equal  volume  of  dis- 
tilled water ;  fasten  the  object  by  means  of  quills  to  the  under  surface  of 
a  cork-stopper,  with  which  the  test-tube  is  then  to  be  securely  closed. 
In  from  ten   to   sixty  minutes,  according  to  the  size  of  the  object,  it  is 
removed  from  the  cork  and  dropped  into  the  fluid  in  the  test-tube.      In 
both  cases  the  objects   remain   in  the  acid  for  twenty-four  hours,  and 
during  this  time  the  containers  must  be  tightly  closed  and  stood  in  the 
dark.     Then  the  objects  are  taken  out,  washed  for  from  one-half  to  two 
hours   in   running   water,   rinsed   in    distilled    water,    and    hardened    in 
gradually  strengthened  alcohols  (§  5). 

8.  Chromic-acetic  osmic  acid  (Flemming's  solution)   (p.    22)  is  an 
excellent  medium  for  the  fixation   of  karyokinetic  figures.     Place  the 
absolutely  fresh,  still  warm  pieces,  from  3  to  5  mm.  in  diameter,  in  4  c.c. 
of  this  fluid,  in  which  they  remain  for  from  one  to  two   days,  or  even 
longer.     Then   the  pieces   should  be  washed  in   running  water  for  one 
hour,  better  longer,  rinsed  in  distilled  water  and   hardened  in  alcohols 
of  gradually  ascending  strength  (§  5).     The  effect  of  this  mixture  on 

*  If,  despite  this,  the  sections  still  show  sublimate  precipitates,  the  latter  may  be  removed 
by  placing  the  sections  in  iodin-alcohol  for  about  ten  minutes.  Then  rinse  them  in  pure  alco- 
hol, transfer  them  to  the  staining  fluid,  etc.  Occasionally,  the  staining  is  difficult ;  this  may  be 
remedied  by  subsequent  treatment  with  diluted  potash  lye  (p.  36,  remark  *). 


THE    PREPARATION    OF    MICROSCOPIC    SPECIMENS.  33 

the  nuclei  is  different  at  the  periphery  of  the  object  than  in  the  interior, 
where  the  chromatin  networks  are  more  distinct,  because  at  the  periphery 
the  osmic  acid,  which  renders  the  nuclear  sap  granular  and  the  nuclear 
reticulum  indistinct,  acts  in  its  purity. 

9.  Platinum-acetic-osmic  acid  mixture  (p.  22)  is  very  suitable  for  dis- 
playing sharply-defined  cell-boundaries.  It  is  used  like  Flemming's 
solution. 

The  fluids  that  have  been  used  for  fixation  cannot  be  employed 
again,  and  should  be  thrown  away. 

§  5.   HARDENING. 

Except  when  alcohol  is  used,  all  the  fixing  methods  necessitate  a 
supplementary  process  of  hardening.  The  best  hardening  medium  is 
alcohol  in  ascending  degrees  of  strength.  Here,  too,  the  rule  is  to  use 
abundance  of  -fluid,  and  to  change  the  alcohol  as  it  becomes  turbid  or 
colored.*  The  exact  application  is  as  follows  :  After  the  objects  have 
been  fixed  in  one  of  the  previously-enumerated  fluids  and  washed  in 
water,f  they  are  placed,  under  exclusion  of  daylight,  for  twelve  hours 
in  50  per  cent,  alcohol,  then  transferred  for  the  same  period  to  70  per 
cent,  alcohol,  and  at  the  expiration  of  this  time  to  90  per  cent,  alcohol 
in  which,  after  another  period  of  from  twenty-four  to  forty-eight  hours, 
the  hardening  is  completed.  In  this  alcohol  the  objects  may  remain  for 
months  before  their  final  preparation.  The  90  per  cent,  alcohol  employed 
for  hardening  should  be  collected  and  used  for  burning,  or  for  hardening 
liver  for  embedding. 

§  6.  DECALCIFYING. 

The  objects  to  be  decalcified  must  not  be  placed  fresh  in  the  decalcify- 
ing fluid  ;  they  must  be  previously  fixed  and  hardened.  For  this  purpose 
place  small  bones  up  to  the  size  of  a  metacarp,  teeth  entire,  and  pieces  from 
3  to  6  cm.  long  sawed  from  the  larger  bones  in  300  c.c.  of  Miiller's  fluid 

*  Objects  fixed  in  chromic  acid  or  in  Miiller's  fluid,  if  not  subjected  to  prolonged  wash- 
ing— and  that  must  be  avoided  because  of  incipient  decomposition — still  yield  substances  to  the 
alcohol,  which  with  the  simultaneous  action  of  daylight  appear  in  the  form  of  precipitates  ;  on 
the  other  hand,  if  the  object  is  kept  in  the  dark  no  precipitates  are  formed,  and  though  the 
alcohol  becomes  yellow  it  remains  clear.  It  is  on  this  account  that  the  exclusion  of  daylight 
has  been  recommended  above  ;  it  is  sufficient  to  place  the  bottles  in  a  dark  part  of  the  room. 
The  90  per  cent,  alcohol  must  be  changed  once  daily  so  long  as  it  becomes  intensely  yellow. 

f  An  exception  is  made  in  the  case  of  objects  that  have  been  fixed  in  picrosulphuric  acid 
and  in  3  per  cent,  nitric  acid.     These  should  be  transferred  directly  from  the  fixing  fluid  to  the 
70  per  cent,  alcohol,  which  must  be  changed  several  times  during  the  first  day. 
3 


34  HISTOLOGY. 

for  from  two  to  four  weeks  and,  after  previous  washing,  harden  them  in 
I  50  c.c.  of  gradually  strengthened  alcohols  (§5).  After  the  bone  has  been 
in  the  90  per  cent,  alcohol  for  three  days  or  longer  it  is  transferred  to  the 
decalcifying  fluid — diluted  nitric  acid,  prepared  by  adding  from  9  to  27 
c.c.  of  pure  nitric  acid  to  300  c.c.  of  distilled  water.  Large  quantities,  at 
least  300  c.c.,  of  this  fluid  should  be  used  and  changed  daily  at  first, 
later  every  four  days,  until  the  decalcification  is  completed.  The  pro- 
cess is  controlled,  and  the  degree  of  decalcification  ascertained,  by  thrust- 
ing in  a  needle  or  by  making  an  incision  with  a  scalpel,  which  should  be 
at  once  carefully  cleaned.  Decalcified  bone  is  flexible,  soft,  and  easily 
cut.  Fetal  bones,  heads  of  embryos,  etc.,  are  decalcified  in  weaker  nitric 
acid  (i  c.c.  of  pure  nitric  acid  to  90  c.c.  of  distilled  water)  or  in  500  c.c. 
of  a  saturated  aqueous  solution  of  picric  acid  (p.  21).  The  process  of 
decalcification  requires  several  weeks  in  the  case  of  thick  bones,  from 
three  to  twelve  days  in  the  case  of  fetal  and  small  bones. 

So  soon  as  the  decalcification  is  completed  the  bones  are  washed  in 
running  water  for  from  six  to  twelve  hours,  and  then  hardened  in  gradu- 
ally strengthened  alcohols  (§  5). 

It  not  infrequently  happens  to  beginners  that  they  transfer  the  bone 
to  alcohol  before  it  is  fully  decalcified,  and  then  in  the  attempt  to  section 
it  they  discover  that  it  is  not  yet  ready  for  use.  In  such  cases  the  entire 
procedure  of  decalcification  must  be  repeated.  If  the  action  of  the  decal- 
cification medium  is  too  prolonged,  it  eventually  leads  to  the  complete 
destruction  of  the  objects. 

§  7.    SECTIONING. 

The  razor  must  be  sharp,  for  success  in  sectioning  depends  upon 
the  sharpness  of  the  knife.  In  cutting,  the  blade  must  be  moistened 
with  alcohol ;  water  is  not  suitable,  because  it  does  not  adhere  evenly  to 
the  surface  of  the  blade.  For  this  purpose  dip  the  knife,  at  each  third 
or  fourth  section,  into  a  shallow  glass  dish  containing  30  c.c.  of  90  per 
cent,  alcohol,  which  at  the  same  time  serves  for  the  reception  of  the  sec- 
tions that  are  cut.  The  razor  is  to  be  held  in  a  horizontal  position, 
grasped  lightly,  with  the  thumb  on  the  side  of  the  cutting  edge,  the 
fingers  toward  the  back  of  the  blade,  the  dorsum  of  the  hand  directed 

o 

upward.  The  object  to  be  sectioned  must  first  have  a  smooth  surface, 
which  is  made  by  cutting  off  a  slice  of  the  necessary  thickness  with  a  single 
movement  of  the  razor.  From  this  surface  the  sections  may  now  be 
taken,  and  should  be  cut  with  a  uniformly  light,  not  too  rapid,  movement, 
as  smooth  as  possible,  and  of  even  thinness.  The  knife  must  not  be 
pushed,  but  should  be  drawn  through  the  object,  .and  that  this  may  be 


THE    PREPARATION    OF    MICROSCOPIC    SPECIMENS.  35 

done  the  portion  of  the  blade  adjoining  the  handle  should  be  first  applied 
to  the  object.  Ten  to  twenty  sections  should  be  made  ;  they  may  be 
transferred  by  means  of  a  needle  or  by  immersing  the  blade  in  the  alco- 
hol.* Then  place  the  dish  on  a  black  surface  and  search  for  the  best  sec- 
tions. The  thinnest 'sections  are  not  always  the  most  useful  ;  for  many 
preparations,  for  example,  for  a  section  through  all  the  coats  of  the 
stomach,  thick  sections  are  to  be  recommended.  For  a  general  view, 
large,  thick  sections  should  be  prepared  ;  for  the  study  of  ultimate  struct- 
ures, thin  sections  ;  for  the  latter  purpose  small  fragments  from  I  to  2 
mm.  on  a  side  are  often  satisfactory. 

If  the  object  to  be  sectioned  is  too  small  to  be  held  with  the  fingers, 
it  should  be  embedded.  The  simplest  method  consists  in  placing  the 
object  in  a  cleft  in  a  piece  of  hardened  liver. 

Ox-liver  or,  better,  human  lardaceous  or  amyloid  liver  may  be 
used.  The  latter  may  be  obtained  from  the  pathologic  laboratories. 
Dog's  liver,  to  be  obtained  from  the  physiologic  laboratory,  is  also 
recommended.  The  liver  should  be  cut  into  pieces  about  3  cm.  high, 
2  cm.  broad,  and  2  cm.  thick,  and  these  hardened  in  90  per  cent,  alcohol, 
which  must  be  changed  within  twenty-four  hours  ;  in  three  to  five  days 
the  liver  attains  the  necessary  hardness.  The  embedding  is  then  accom- 
plished by  making  an  incision  in  one  of  these  pieces  from  the  top  half-way 
down  and  inserting  the  object  into  the  cleft  thus  made.  If  the  object  is 
too  thick,  furrows  can  be  cut  in  the  liver  with  a  small  scalpel  and  the 
object  fitted  into  these.  The  object  requires  no  further  staying  except, 
perhaps,  binding  with  thread. 

As  a  rule  I  embed  objects  in  liver ;  very  thin  sections  can  then  be 
made  so  soon  as  one  has  a  certain  amount  of  skill,  and  this  can  be  easily 
acquired  in  the  course  of  a  few  weeks. 


§  8.  STAINING. 

Before  using  a  stain  it  should  always  be  filtered.  A  small  funnel 
may  be  made  by  simply  twice  folding  a  piece  of  filter-paper  5  cm.  square 
and  supporting  it  in  a  cork  frame,  which  can  be  made  by  cutting  out  a 
piece  2  cm.  square  from  a  cork  plate  5  cm.  square.  The  frame  is  then 
mounted  on  four  long  pins.  Such  a  funnel  and  frame  can  be  used  re- 
peatedly, but  only  for  the  same  fluid.  The  sections  should  not  float 
on  the  surface  of  the  staining  fluid  ;  they  should  be  submerged  with 
needles. 

*  Very  thin  sections  that  are  not  to  be  stained  or  that  have  been  stained  in  bulk  may  be 
transferred  directly  to  the  slide  by  inclining  the  blade  and  slipping  or  rinsing  them  off. 


36  HISTOLOGY. 

1.  Nuclear  Staining  with  Hanseii  s  Hematoxylin  (p.  23). — Filter  from 

3  to  4  c.c.  of  the  staining  fluid  into  a  watch-glass  and  in  it  place  the  sec- 
tions.    The  time  in  which  the   sections   stain  varies  greatly.     Sections 
fixed  and  hardened  in  alcohol  stain  in  from  one  to  three  minutes.     If 
Miiller's  fluid  was  used  for  fixing,  the  sections  must  remain  in  the  staining 
fluid  somewhat  longer — up  to  five  minutes.* 

From  the  stain  the  sections  are  transferred  to  a  watch-glass  contain- 
ing distilled  water,  in  which  they  are  washed, — i.  e.,  gently  moved  about 
with  the  needle  to  remove  the  excess  of  dye, — and  then  placed  in  a  glass 
containing  30  c.c.  of  distilled  water.  In  this  the  sections  must  remain  at 
least  five  minutes,  during  which  their  blue-red  color  changes  to  a  beauti- 
ful deep  blue,  which  becomes  the  purer  the  longer  (up  to  twenty-four 
hours)  the  sections  are  allowed  to  remain  in  the  water.  At  first  the  sec- 
tions have  a  faded  blue  tint ;  usually  the  differentiation  occurs  in  about 
five  minutes,  but  sometimes  not  for  hours.  When  it  is  completed,  certain 
details  can  be  recognized  even  by  the  unaided  eye. 

Beginners  are  recommended  to  leave  the  sections  for  different  lengths 
of  time — one,  three,  or  five  minutes — in  the  stain,  in  order  to  learn  the 
time  required  to  produce  successful  staining.  The  chief  essential  in 
hematoxylin  staining  is  thorough  washing  ;  if  the  water  becomes  blue,  it 
must  be  replaced  by  fresh.  The  used  stain  should  be  poured  back 
through  the  filter  into  the  hematoxylin  bottle.  The  watch-glasses 
should  be  immediately  cleaned. 

2.  Nuclear  Staining  with  Alum-carmine  (p.  24). — Filter  from  3  to 

4  c.c.  of  the  staining  fluid  into  a  watch-glass,  place  the  sections  in  it,  and 
allow  them  to  stain  for  at  least  five  minutes.     The  advantage  of  this  dye 
lies  in  this,  that  the  sections  may  be  left  in  it  for  a  longer  period  without 
becoming   overstained,  what  is  more  apt  to  occur  with  hematoxylin  ;  a 
disadvantage   is,   that    alum-carmine    is    a  pure   nuclear   stain,  while  in 
hematoxylin  staining  the  protoplasm  too  acquires  color,  a  gray  or  gray- 
violet  tone,  and  is  thereby  more  easily  recognized. 

3.  Diffuse  Staining. — For  staining  the  protoplasm  and  the  inter- 
cellular substances. 

(a)    Slow  Staining. — A   small  drop  of  neutral  carmine  solution  is 

*  Sections  fixed  in  the  strong  solution  of  chromic  acid  or  in  Zenker's  fluid,  or  objects  not 
entirely  free  from  acid,  often  stain  very  slowly,  occasionally  not  at  all.  This  defect  can  be  reme- 
died either  by  keeping  the  objects  from  two>  to  three  months  in  90  per  cent,  alcohol,  which  must 
be  changed  two  or  three  times  during  this  period ;  or  by  treating  the  sections  from  five  to  ten 
minutes  with  5  c.c.  of  distilled  water  to  which  from  3  to  7  drops  of  35  per  cent,  solution 
of  potassium  hydroxid  have  been  added.  The  sections  are  then  to  be  transferred  for  from  one 
to  two  minutes  to  a  watch-glass  containing  pure  distilled  water,  and  from  this  into  the  hema- 
toxylin. In  from  five  to  ten  minutes  such  sections  will  also  stain. 


THE    PREPARATION    OF    MICROSCOPIC    SPECIMENS.  37 

transferred  by  means  of  a  glass-rod  to  a  capsule  containing  20  c.c.  of  dis- 
tilled water,  on  the  bottom  of  which  lies  a  small  piece  of  filter-paper.* 
The  sections  remain  over  night  in  this  fluid.  The  paler  the  rose-color  of 
the  fluid,  the  longer  the  time  required  for  staining  and  the  more  beautiful 
the  result  will  be.  The  beginner  is  always  inclined  to  regard  the  pale- 
rose  fluid  as  too  dilute  to  secure  good  staining,  until  on  the  following 
day  the  deep  pink  to  red  sections  teach  him  better. 

This  stain  can  be  used  alone  only  in  a  few  cases,  but  is  highly 
recommended  for  double-staining.  The  sections  should  be  stained  first 
with  the  carmine  solution,  then  with  hematoxylin. 

(&)  Rapid  Staining. — Add  10  drops  of  a  solution  of  eosin  (p.  25) 
to  3  or  4  c.c.  of  distilled  water.  In  this  the  sections  remain  for  from  one 
to  five  minutes,  are  then  washed  in  distilled  water,  and  then  placed  in 
30  c.c.  of  fresh  distilled  water  (see  No.  I,  p.  36).  The  stain  may 
be  used  alone  or  combined  with  hematoxylin  ;  in  the  latter  case  the 
whole  procedure  of  hematoxylin  staining  is  to  be  carried  out  first,  and 
then  that  of  eosin  staining. 

4.  Staining  of  the   Chromatin  Substance    (for  nuclear  division). — 
Place  the  objects  for  from  five  to  ten  minutes  in  a  watch-glass  containing 
i  o  c.c.  of  distilled  water  and  one  drop  of  pure  hydrochloric  acid ;  wash  them 
for  one  minute  in  distilled  water  and  transfer  them  to  a  watch-glassful  of 
safranin   solution  (p.    25),  in   which   they   should   remain   five   minutes. 
The  sections  or  membranes  are  then  lifted  out  with  the  needle  and  placed 
in  about  5  c.c.  of  absolute  alcohol  for  decolorization.     When  the  sections 
no  longer  give  off  much  of  the  dye  (usually  in  from  one  to  two  minutes) 
they  are  transferred   to   5  c.c.  of  fresh  absolute  alcohol  for  one  minute, 
then  cleared  and  mounted  (§  10,  3,  p.  45).      If  the  immersion  in  absolute 
alcohol  is  too  prolonged,  it  may  lead  to  total  decolorization  of  the  prep- 
aration.      Failure  in  staining  is  usually  due  to  an  insufficient  amount  of 
acetic  acid  in  the  Flemming's  solution  (p.  22,  remark). 

5.  Staining  in  Bulk.^ — (Nuclear  staining  of  the  entire  object  before 
sectioning.) — The  fixed  and  hardened  objects  are  placed  in  30  c.c.  of  borax- 
carmine  for  twenty-four  hours  if  they  are  small  (5  mm.  square),  for  from 
two  to  three  days  if  they  are   larger.      From  this  they  are  transferred 
directly  to  25  c.c.  of  acid-alcohol  (p.  25);  the  used  borax-carmine  may 

*  If  the  filter-paper  is  omitted  the  sections  stain  only  on  the  one  side. 

f  Editor's  remark:  It  is  especially  for  staining  in  bulk  that  alum- cochineal  (recom- 
mended on  p.  25,  remark)  proves  very  useful.  It  has  the  advantage  of  not  overstaining,  and 
does  not  need  in  its  application  a  special  discharging  fluid.  Stain  the  pieces  for  about  twenty- 
four  hours  and  wash  them  in  several  changes  of  water  to  remove  the  excess  of  stain  and  the 
alum  ;  then  transfer  to  alcohol  of  gradually  increased  strength. 


38  HISTOLOGY. 

be  returned  to  the  bottle.  In  a  few  minutes  the  acid-alcohol  acquires  a 
red  color  *  and  must  be  replaced  by  fresh,  which  should  be  again 
renewed  in  about  fifteen  minutes  ;  this  renewal  must  be  repeated  until 
the  alcohol  no  longer  becomes  red.  f  The  object  is  then  transferred 
to  90  per  cent,  alcohol,  and  if  after  twenty-four  hours  it  is  not  suffi- 
ciently hardened  to  be  sectioned,  it  is  placed  for  twenty-four  hours  or 
longer  in  absolute  alcohol. 

6.  Picrocarmine, — Double-staining  :  Nuclei  and  connective  tissue  red, 
protoplasm  yellow.      Filter  about  5  c.c.  of  the  staining  fluid  into  a  watch- 
glass.     The  length  of  time  in  which  picrocarmine  acts  differs  greatly  for 
individual   objects   and    can  be  approximately  given  only  in  the  special 
directions.     When  the  staining  is  completed,  the  dye  is  filtered  back  into 
the  bottle  and  the  object  transferred  for  from  ten  to  thirty  minutes  to  10 
c.c.  of  distilled  water.     (The  latter  procedure  is  omitted  in  staining  under 
the  cover-glass,  p.  48.)     If  the  object,  e.  g.,  a  section,  is   to   be  dehy- 
drated in  absolute  alcohol  (p.  45),  it  must  not  be  allowed  to  remain  in 
this  reagent  longer  than  from  one  to  two   minutes,  because  the  alcohol 
extracts  the  yellow  stain  ;  or,  the  decolorization   can  be  prevented   by 
adding  a  small  crystal  of  picric  acid  to  the  absolute  alcohol. 

Picrocarmine  is  preferably  used  in  the  examination  of  fresh  objects. 
If  the  solution  is  good,  very  pretty  staining  is  obtained  that  is  improved 
by  subsequent  treatment  with  acidulated  glycerol,  which  renders  it  crisp 
and  clear. 

7.  Nuclear  Staining  zvith  Anilin  Dyes. — For  this  purpose  the  best 
anilin  dyes  are  vesuvin  and   methyl-violet,  B  (p.  25).     Filter  5  c.c.  of  the 
staining  fluid  into  a  watch-glass  ;  in  this  place  the  sections,  which  acquire 
a  very  dark  color  in  from  two  to  five  minutes  ;  they  are  then  washed  in, 
distilled   water    and   transferred    to    a   watch-glass    containing    absolute 
alcohol,  in  which  they  give  off  the  dye  abundantly.     In  a  few  minutes, 
from    three  to   five,   the    sections    become   paler,   and    individual    parts 
(e.  g.,  the  glands  of  the  skin)  can  be  detected  by  the  unaided  eye.     The 
sections  are   now  to  be  transferred  to  another  watch-glass  containing 
5  c.c.  of  absolute  alcohol,  and  in  about  two  minutes  they  may  be  cleared 
and  mounted.     The   result  is  a  very  beautiful  permanent  nuclear  stain. 
A  disadvantage  lies  in  the  necessity  for  using  so  much  absolute  alcohol. 

Safranin  can  be  similarly  employed.     The  sections  stained  for  five 

*  Preparations  fixed  in  Muller's  fluid  often  give  off  very  little  dye. 

f  This  may  require  from  one  to  three  days ;  during  the  first  day  the  fluid  should  be 
changed  every  two  hours,  subsequently  every  four  hours.  If  you  wish  to  be  economical, 
take  a  needle  and  gently  push  the  object  out  of  the  area  of  red  fluid  in  which  it  lies  into 
uncolored  portion  of  the  alcohol. 


THE    PREPARATION    OF    MICROSCOPIC    SPECIMENS.  39 

minutes  are  washed  for  thirty  seconds  in  a  watch-glass  containing  95  per 
cent,  alcohol  and  then  transferred  to  absolute  alcohol,  which  must  be 
replaced  by  fresh  so  soon  as  it  becomes  intensely  red.  In  from  five  to 
fifteen  minutes — the  time  varies  according  to  the  thickness  of  the  sec- 
tions— they  are  sufficiently  decolorized  and  are  then  to  be  cleared  in  oil 
and  mounted  in  damar-varnish  (p.  45). 

8.  Methylcne-blue    for  Staining  Axis-cylinders. — This    method    is 
applicable  only  to  perfectly  fresh  preparations.      Prepare  a  TU  per  cent, 
solution,  which  may  be  done  by  adding   I  c.c.  of  a   I   per  cent,  solution 
(p.  25)  to  15  c.c.  of  distilled  water.      The  fresh  preparation  is  treated  on 
the  slide  with  a  few  drops  of  the  diluted  staining  fluid,  and  meanwhile 
protected  with  a  watch-glass,  which  must  not  be  so  applied  as  to  make 
an  hermetic  cover,  since  the  access  of  atmospheric  air  is  necessary  to  the 
success  of  the  staining.     The  reaction  occurs  in  from  one  to  one-and-a- 
half  hours,  and  can  be  rendered  more  certain  by  gently  moving  the  prep- 
aration to   and  fro.      In  order  to  prevent  the  drying  of  the  preparation 
during  this  period,  a  drop  of  the  diluted  staining  fluid  or  of  normal  salt 
solution  should  be  added  from  time  to  time.     When  the  staining  is  done, 
a  cover-glass  should  be  applied.    The  result  is  a  beautiful  blue  coloration 
of  the  axis-cylinders.     Other  elements  often  are  stained,  the  nuclei,  con- 
nective-tissue fibers,  etc.,  and  with  more  prolonged  action  of  the  reagent 
also  the  medullary  sheaths  of  the  nerves.     The  preparation  may  be  pre- 
served as  follows  :  replace  the  staining  fluid  with  a  drop  of  ammonium 
picrate  solution  (p.  25)  according  to  the  method  given  on  p.  48  ;  this 
converts  the  blue  color  to  violet ;  then  place  a  drop  of  glycerol  at  the 
edge  of  the  cover-glass,  and  it  will  gradually  take  the  place  of  the  evap- 
orating water  of   the   ammonia  solution,  and  thus  make  the  specimen 
permanent. 

After  eighteen  to  twenty  hours  secure  the  cover-glass  with  cement 
(p.  45).  The  preparations  must  not  be  exposed  to  sunlight,  in  which 
they  fade  ;  in  any  case  they  soon  lose  their  original  beauty. 

9.  Delafield '  s  Hematoxylin  for  Staining  Mucus. — Filter  three  drops 
of  this   fluid   (p.  23)   into  a  watch-glass   containing   25    c.c.  of  distilled 
water.      In  this  dilute  solution  the  sections  (preferably  of  objects  fixed  in 
Flemming's   mixture*)  are  placed  and  remain  for  two  or  three  hours. 
Usually  at  the  end  of  this  period  the  mucus  (e.  g.,  in  the  goblet-cells)  is 
stained  an  intense  blue,  which  can  be  ascertained  by  examining  with  low 
magnification  the  sections  as  they  lie  in  the  solution.      It  is  often  neces- 


*  Preparations  that  have  been  fixed  in  Miiller's  and  in  Zenker's  fluid  are  also  suitable  for 
mucus-staining. 


4O  HISTOLOGY. 

sary  for  the  sections  to  remain  in  the  solution  for  a  longer  time.  Then 
they  are  washed  for  one  minute  and  mounted  in  damar,  according  to  the 
rules  given  in  §10,  3,  p.  45.  The  nuclei  also  stain  blue.  Very  pretty 
pictures  are  obtained  by  a  combination  with  safranin  and  picric  acid,  as 
in  No.  10. 

10.  Triple -staining  is  accomplished  in  the  following  manner  :    The 
sections  stained  in  Delafield's  hematoxylin  are  placed  for  five  minutes  in 
safranin  (p.    25)  and  then  transferred  to  5  c.c.  of  absolute  alcohol,  which 
must  be  changed  twice  within  fifteen  minutes.     The  sections  are  next 
placegl  for  one  minute  in  5  c.c.  of  absolute  alcohol,  to  which  five  drops 
of  a  saturated  alcoholic  solution  of  picric  acid  have  been  added  (i'gm.  of 
picric  acid  to  15  c.c.  of  absolute  alcohol),  washed  for  thirty  seconds   in 
pure  absolute  alcohol,  and  mounted  in  damar  (§  10,  3,  p.  45). 

Result :  mucus,  blue  ;  nuclei,  red  ;  protoplasm  and  fibers,  yellow. 

11.  Staining  of  Elastic  Fibers. — Sections  of  objects  fixed    in  any 
medium  are   placed  in  5  c.c.  of  a  solution  of  orcein   (p.   25),  and  after 
about  fifteen  hours  are  decolorized  in  10  c.c.  of  acid-alcohol  (see  Borax- 
carmine,  p.  24),  in  which  they  remain  for  from  twenty  to  sixty  minutes, 
according  to  their  thickness.      If  they  are  left  too  long  in  the  acid-alco- 
hol the  dye  is  extracted  from  the  fine  elastic  fibers.     Therefore  the  pro- 
cess of  decolorization  should   be   controlled   by  frequent  examination  of 
the  sections.      In  successful  preparations  the  elastic  fibers  appear  brown- 
red  on  a  light  background. 

12.  Silver  Staining. — For  the  exhibition  of  cell-boundaries  and  the 
staining  of  intercellular  cement-substance.* 

The  use  of  metallic  instruments  must  be  avoided  ;  glass-rods  should 
be  employed,  and  quills  instead  of  pins. 

The  object  is  immersed  for  from  one-half  to  ten  minutes,  according 
to  its  thickness,  in  10  to  20  c.c.  of  a  I  per  cent,  or  weaker  (see  Special 
Technic)  solution  of  silver  nitrate  (p.  22),  which  meanwhile  becomes 
milky  and  turbid  ;  it  is  then  removed  with  glass-rods,  washed,  placed  in 
a  porcelain  capsule  containing  100  c.c.  of  distilled  water,  and  exposed  to 
direct  sunlight  ;  in  a  few  minutes  a  faint  brown  coloration  appears — the 
sign  of  a  successful  reduction.  So  soon  as  the  object  has  become  a 
deep  red-brown  (usually  in  from  five  to  ten  minutes)  it  is  taken  out, 
placed  in  a  watch-glass  containing  distilled  water  to  which  a  few  grains  of 
common  salt  have  been  added,  and  at  the  end  of  five  or  ten  minutes 
transferred  to  30  c.c.  of  70  per  cent,  alcohol,  and  stood  in  the  dark  ;  in 


*  The  cross-striations  that  appear  in  different  tissues  and  organs,  when  treated  with  silver 
nitrate,  particularly  in  nerve-fibers,  blood-vessels,  cartilages,  etc.,  are  artefacts. 


THE    PREPARATION    OF    MICROSCOPIC    SPECIMENS.  4! 

from  three  to  ten  hours  the  70  per  cent,  should  be  replaced  by  90  per 
cent,  alcohol.  The  immersion  in  the  silver  solution  should  be  .done 
under  exclusion  of  sunlight ;  the  reduction,  on  the  other  hand,  should 
be  undertaken  only  with  sunlight*  If  the  sun  does  not  shine,  the  object, 
after  treatment  with  the  silver  solution  and  washing  in  distilled  water,  is 
to  be  preserved  in  the  dark  in  30  c.c.  of  70  per  cent,  (later  90  per  cent.) 
alcohol,  and  in  this  exposed  to  sunlight  at  the  earliest  opportunity. 

13.  Golgi's  "black"  reaction  for  demonstration  of  the  elements 
of  the  nervous  system,  f 

This  method  unites  fixing  and  staining.  The  objects  must  be  as 
fresh  as  possible,  and  in  general  their  diameter  should  not  exceed 
4  mm.  It  is  not  easy  to  cut  fresh  brain  into  pieces  of  this  size  with- 
out bruising  the  delicate  tissue  ;  therefore  place  larger  pieces  (up  to 

3  cm.  cubes)  in   a  small  glass  jar   containing  freshly  prepared    Golgi's 
mixture  (p.  21),  which  is  to  be  covered  and  stood  in  the  dark  (in  winter 
it  must  be  put  in  an    oven  having  a  temperature  of  about  25°  C).      In 
from  one    to    two  hours   the  pieces  can  easily  be  cut  into  slices  about 

4  mm.  in  diameter.     The  quantity  of  Golgi's  fluid  to  be  used  is  regulated 
by  the  number  of  the   slices,  each   slice  requiring   about    10  c.c.  of  the 
mixture.      In  from  two  to  six  days,  less  often  fifteen  days,J   the  slices 
are  taken  out,  quickly  washed  for  a  couple  of  seconds  in  distilled  water, 
gently  dried  with  filter-paper,  and  placed  in  0.75  per  cent,  silver  solution 
(30   c.c.  of  the    I    per    cent,    solution  [p.  22]    plus    10   c.c.  of  distilled 


*The  reduction  takes  place  in  ordinary  daylight,  but  slowly,  and  yields  less  satisfactory 
results. 

f  Editor's  remark  :  In  American  laboratories  a  modification  of  Golgi's  method  by  Cox  is 
often  used  with  excellent  results.  This  modification  is  particularly  recommended  to  beginners, 
because  it  is  very  simple  and  nearly  always  successful.  In  its  application  the  following  direc- 
tions should  be  observed :  Put  small  cubes,  2  cm.  or  less,  of  the  organs  of  the  central  nervous 
system  of  adult  or  newborn  animals  for  from  six  to  ten  weeks  into  the  Cox-Golgi  mixture,  the 
formula  of  which  is  given  on  p.  21  (No.  15),  using  IO  to  20  times  the  volume  of  the  object 
treated.  Change  the  fluid  at  the  following  intervals  :  after  twenty-four  hours  ;  three  days  ;  eight 
days;  fifteen  days ;  twenty-one  days;  thirty  days.  The  objects  should  remain  in  the  mixture 
until  they  are  to  be  sectioned,  and  will  keep  in  good  condition  for  about  ten  months.  Then 
transfer  them  directly  into  95  per  cent,  alcohol  for  one  hour  ;  into  alcohol-ether  (equal  parts) 
for  a  half  hour  ;  into  thin  celloidin  solution  (in  alcohol-ether)  for  one  hour.  Mount  on  a  block 
with  thick  celloidin  solution  (see  Microtome  Technic)  and  harden  in  80  per  cent,  alcohol 
for  from  one  to  two  hours.  Cut  at  once  sections  from  50  to  100  //  thick  ;  clear  them  in  a  mixture 
of  xylol,  three  parts,  and  carbolic  acid,  one  part,  in  which  they  may  remain  for  weeks  without 
injury.  Mount  in  balsam  and  ewer  the  sections  vvith  a  cover-glass.  In  time  the  specimens  thus 
preserved  are  not  infrequently  marred  by  the  appearance  of  corrosive  crystals,  but  the  impreg- 
nation of  the  elements  of  the  nervous  tissue  remains  intact. 

%  See  Special  Technic. 


42  HISTOLOGY. 

water,  and  for  each  piece  10  c.c.  of  this  fluid).*  A  brown  precipitate 
immediately  surrounds  the  pieces.  They  should  be  left  in  the  silver- 
solution  for  two  days  (which  need  not  stand  in  the  dark  and  must  not 
be  placed  in  the  oven),  and  they  may  remain  in  it  for  six  days  without 
injury  ;  they  are  then  placed  for  from  fifteen  to  twenty  minutes  (not 
longer)  in  20  c.c.  of  absolute  alcohol,  then  embedded  in  elder-pith  (or 
in  celloidin,  see  Microtome  Technic)  and  cut  into  thick  sections  (p.  34). 

Each  section  should  be  examined,  without  a  cover-glass,  with  the 
low  power,  in  order  to  ascertain  its  usefulness  ;  if  it  is  good,  it  is  placed 
for  from  one  to  two  minutes  in  a  watch-glass  containing  absolute  alcohol, 
then  in  creosote  for  two  minutes,  and  in  oil  of  bergamotfor  two  minutes  ; 
from  this  it  is  transferred  for  a  few  seconds  to  xylol,  then  placed  upon 
the  slide.  Finally  the  xylol  is  removed  by  light  pressure  on  the  section 
with  clean  filter-paper  and  the  preparation  covered  with  a  few  drops  of 
Canada-balsam  diluted  with  xylol.  A  cover-glass  must  not  be  applied, 
because  it  would  prevent  evaporation  of  the  moisture  in  the  section, 
which  when  retained  destroys  the  Golgi  preparations.  Not  infrequently 
— especially  when  the  xylol  has  not  been  satisfactorily  removed — the 
Canada-balsam  gradually  withdraws  from  the  preparation,  which  in  con- 
sequence appears  spoiled,  but  may  be  fully  restored  by  the  application  of 
a  fresh  drop  of  balsam.  At  first  the  preparation  should  be  examined 
with  the  low-power  objective  ;  when  the  balsam  has  become  dry  the 
high  power  may  be  used. 

The  results  obtained  by  this  method,  when  successful,  are  admir- 
able ;  single  elements  of  the  nervous  system  (never  all),  occasionally  also 
blood-vessels,  lymph-vessels,  connective-tissue  fibers,  secretions,  muscle- 
fibers,  and  epithelial-cells  stand  out  in  full  relief — black  on  a  light  back- 
ground. But  the  method  is  subject  to  various  accidents.  Almost  in- 
variably the  best  sections  are  disfigured  by  black  precipitates  ;  these  occur 
chiefly  at  the  edges  of  the  preparations  ;  in  order  to  avoid  them  it  has 
been  suggested  that  a  layer  of  coagulated  blood  be  applied  to  the  fresh 
object.  Very  often  the  reaction  fails  entirely  (especially  when  the  action 
of  the  Golgi  mixture  was  too  prolonged);  then  the  so-called  "double 
method"  may  lead  to  success.  If  the  first  sections  show  nothing,  the 
objects  should  be  again  treated  with  Golgi's  fluid  for  from  twenty-four  to 
thirty-six  hours,  and  for  the  same  length  of  time  with  the  silver  solu- 
tion. A  second  failure  may  be  occasionally  crowned  with  success  by  a 
second  repetition  of  the  procedure.  In  the  application  of  Golgi's  method 
practice  and  patience  are  important  factors. 


*The  used  Golgi  mixture  is  to  be  thrown  away. 


THE    PREPARATION    OF    MICROSCOPIC    SPECIMENS.  43 

Preparations  to  which  the  foregoing  method  has  been  applied  can 
be  "  fixed."  For  this  purpose  the  sections  are  transferred  from  the 
alcohol  to  a  mixture  of  10  c.c.  of  absolute  alcohol*  and  20  c.c.  of 
the  diluted  solution  of  hydrochinone  (p.  21);  in  this  they  remain  five 
minutes,  during  which  they  become  dark  gray  to  black.  When  the 
reduction  is  completed,  the  sections  are  directly  transferred  for  from  ten 
to  fifteen  minutes  to  a  glass  containing  70  per  cent,  alcohol.  In  this 
they  become  paler,  then  are  placed  in  the  sodium-hyposulphite  solution 
(p.  21)  for  five  minutes,  and  finally  in  a  large  capsule  containing  distilled 
water,  in  which  they  must  remain  at  least  twenty-four  hours  or  longer. 
The  preparations  that  have  been,  thus  "  fixed  "  can  be  mounted,  like 
other  preparations,  under  a  cover-glass,  and  staining  with  alum-carmine 
or  hematoxylin  is  sometimes  successful. 

14.  Gold  Staining,  for  the  demonstration  of  nerve  terminations. — 
Steel  instruments  must  not  be  used  ;  all  manipulations  in  the  gold  solu- 
tion are  to  be  performed  with  rods  of  glass  or  wood.  Put  8  c.c.  of  a 
I  per  cent,  gold-chlorid  solution  and  2  c.c.  of  formic  acid  into  a  test-tube 
and  heat  the  mixture  to  the  boiling-point ;  let  it  boil  up  three  times. 
Into  the  cooled  mixture  very  small  cubes  of  tissue  (at  most  5  mm.  square) 
are  placed  for  one  hour,  during  which  they  must  be  kept  in  the  dark  ; 
then  they  are  washed  in  distilled  water  and  exposed  to  the  light  in  a 
mixture  of  formic  acid,  10  c.c.,  and  distilled  water,  40  c.c.  Sunlight  is 
not  necessary.  The  reduction  takes  place  slowly,  often  not  until  after 
twenty-four  or  forty-eight  hours,  the  exterior  of  the  cubes  meanwhile 
assuming  a  dark-violet  hue.  When  the  reduction  is  completed,  place  the 
tissue  in  30  c.c.  of  70  per  cent,  alcohol  and  on  the  following  day  in  an 
equal  quantity  of  90  per  cent,  alcohol,  in  which,  to  hinder  further  reduc- 
tion, they  must  remain  in  the  dark  for  at  least  eight  days  before  their  final 
preparation. 

§  9.   INJECTING. 

The  filling  of  the  blood-  and  lymph-vessels  with  colored  masses  is 
a  special  art  that  can  only  be  acquired  through  much  practice.  The 
knowledge  of  the  many  little  devices  employed  can  scarcely  be  attained 
through  didactic  teaching,  however  painstaking  and  explicit.  Here  prac- 
tical instruction  is  indispensable.  Accordingly,  since  this  book  is  intended 
for  beginners,  it  seems  wise  to  refrain  from  entering  upon  a  detailed 
account  of  the  technic  of  injecting. 

*  Excess  of  alcohol  produces  a  precipitate,  which  can  be  promptly  removed  by  the  addi- 
tion of  more  hydrochinone  solution. 


44  HISTOLOGY. 

He  who  desires  to  attempt  injecting  must  have  an  accurately-closing, 
smoothly-working  hand-syringe,  provided  with  cannulae  of  different  sizes. 
For  an  injecting  mass  Berlin  blue  (Griibler)  is  recommended — 3  gm.  dis 
solved  in  600  c.c.  of  distilled  water.  It  is  advisable  to  begin  with  the 
injection  of  single  organs — for  example,  the  liver,  which  is  preferable 
because  it  gives  useful  results,  even  though  the  blood-vessels  are  but 
partially  filled.  The  injected  object  should  be  fixed  for  from  two  to  four 
weeks  in  Miiller's  fluid  (p.  31)  and  hardened  in  gradually  strengthened 
alcohols  (p.  33).  The  sections  should  not  be  very  thin. 


§  10.   MOUNTING  AND  PRESERVING   OF  THE 
PREPARATIONS. 

The  finished  sections  and  other  objects  prepared  according  to  the 
foregoing  methods,  in  order  that  they  may  be  examined  under  the  micro- 
scope, are  finally  mounted  on  a  slide  and  covered  with  a  cover-glass. 
The  media  in  which  the  sections  are  mounted  are  :  (i)  water ;  or,  if  the 
section  is  to  be  cleared  and  preserved,  (2)  glycerol ;  or  (3)  damar- 
varnish. 

The  transfer  of  the  object  to  the  slide  is  usually  done  in  this  way  : 
a  small  drop  of  a  suitable  fluid  is  placed  on  the  middle  of  the  slide  ;  the 
section  is  then  taken  up  on  the  section-lifter,  and  with  the  aid  of  the 
needle  slipped  off  onto  the  slide.  Very  thin  sections  are  better  lifted  on 
the  end  of  a  glass-rod,  and  by  rolling  of  the  latter  transferred  to  the 
slide.  When  the  section  is  smoothly  mounted,  it  is  covered  with  a 
cover-glass.*  The  latter  must  be  grasped  by  its  edges,  not  by  its  sur- 
faces. It  should  be  taken  in  the  left  hand,  'one  edge  placed  in  contact 
with  the  slide,  and  then,  supported  on  its  under  surface  by  a  needle  held 
in  the  right  hand,  slowly  lowered  upon  the  preparation.  It  is  simpler 
to  suspend  a  drop  of  the  mounting  medium  from  the  inferior  surface  of 
the  cover-glass  and  then  to  let  it  softly  fall  upon  the  preparation. 
The  fluid  in  which  the  section  is  mounted  must  occupy  the  entire  space 
between  cover-glass  and  slide.  If  the  amount  of  fluid  is  insufficient, 
another  drop  should  be  placed  at  one  edge  of  the  cover-glass  by  means 
of  a  glass-rod.  If  there  is  too  much  fluid — and  here  the  beginner 

*  Examinations  with  low  powers,  without  a  cover-glass,  are  permissible  only  for  the  most 
superficial  orientation  ;  e.  g.,  to  ascertain  if  an  object  has  been  sufficiently  teased.  In  all  other 
cases  the  cover-glass  is  indispensable.  In  order  to  convince  one's  self  of  this  an  uncovered  sec- 
tion should  be  examined,  then  covered  with  a  cover-glass,  and  examined  again.  Many  a  good 
preparation  that  one  neglects  to  cover  appears  useless.  Examinations  with  high-power  objec 
tives  without  a  cover-glass  are  in  general  not  allowable. 


THE    PREPARATION    OF    MICROSCOPIC    SPECIMENS.  45 

strives  to  perpetrate  impossibilities — the  excess  which  has  escaped  from 
beneath  the  edges  of  the  cover-glass  should  be  absorbed  with  filter-paper. 
The  upper  surface  of  the  cover-glass  must  always  be  dry.  Small  air-bub- 
bles under  the  cover-glass  may  be  removed  by  cautiously  raising  and 
lowering  the  cover-glass  several  times  with  the  needle  (see  further,  p.  46). 

1 .  The  examination  of  the  unstained  and  the  stained  sections  in  water 
or  normal  salt-solution  should  never  be  neglected,  since  many  structural 
peculiarities — for  example,  connective-tissue  formations — stand  out  dis- 
tinctly in  these  media,  which  under  the  clearing  influence  of  glycerol  or 
damar-varnish  almost  entirely  elude  observation.      Preparations  mounted 
in  water  or  salt-solution  cannot  be  preserved. 

2.  Preparations  mounted  in  glycerol  can  be  preserved ;  in  order  to  pre- 
vent the  shifting  of  the  cover-glass  it  should  be  secured  with  cover-glass 
cement  (p.  23).     The   edge   of  the   cover-glass  must  be  perfectly  dry  ; 
this  is  an  indispensable  preliminary  condition,  because  the  cement  adheres 
only  to  a  dry  glass  surface.     The  drying  is  accomplished  in  this  wise  : 
remove   the  excess   of  glycerol  surrounding  the  cover-glass  with  filter- 
paper   and  then,   with  a   cloth   moistened  in  90  per   cent,   alcohol  and 
turned  over  the  finger-tip,  carefully  wipe  the  slide  clean  all  around  the 
cover-glass  without  disturbing  the  latter.      Now  heat  a  glass-rod  and  dip 
it  into  the  hard  cement  ;*  place  a  drop  at  each  corner  of  the  cover-glass 
and  trace  a  continuous  border  from  I  to  3  mm.  wide,  in  such  a  way  that 
one  edge  rests  on  the  cover-glass,  the  other  on  the  slide.      Finally,  heat 
the  rod  again  and  smooth  the  surface  of  the  band  of  cement. f 

Preparations  mounted  in  glycerol  often  do  not  become  transparent 
until  the  second  or  third  day.  Hematoxylin  and  other  dyes  soon  fade 
in  it  ;  picrocarmine  and  carmine,  on  the  contrary,  are  permanent. 

3.  The  mounting  of  objects  in  damar-varnish  is  the  most  popular  pre- 
serving method.      In  comparison  with  glycerol  it  has  the  advantage  of 
keeping  the  colors,  but  has  one  disadvantage  ;  it  clears  more  vigorously 
than  diluted  glycerol,  and  thus   renders   many  delicate  structures  com- 
pletely invisible.   Sections  in  alcohol  or  water  cannot  without  further  treat- 
ment be  mounted  in  damar-varnish, — they  must  be  previously  dehydrated. 
For  this  purpose  the  sections  are  lifted  with  a  needle  (very  thin  sections  with 
needle  and  section-lifter)  and  placed  in  a  covered  watch-glass  containing 

*  Glass-rods  fracture  very  easily  in  this  procedure,  nevertheless  are  preferable  to  metal 
rods,  because  the  latter  cool  too  quickly.  The  fracturing  can  be  prevented  in  a  measure  by 
heating  the  glass-rod  to  red  heat,  meanwhile  turning  it  continuously ;  only  rods  insufficiently 
annealed  break  when  they  are  dipped  into  the  cement. 

^Editor's  remark:  King's  fluid  cover-glass  cement  (p.  23,  foot-note)  is  to  be  applied 
with  a  small  brush. 


46  HISTOLOGY. 

5  c.c.  of  95  per  cent,  alcohol.  In  making  this  transfer,  as  little  as 
possible  of  the  water  should  be  allowed  to  adhere  to  the  section.  If  a 
section-lifter  is  used  the  water  clinging  to  it  should  be  absorbed  with  filter- 
paper  ;  if  the  sections  are  lifted  on  a  needle  the  water  can  be  removed  by 
bringing  the  filter-paper  into  gentle  contact  with  them.  Thin  sections  re- 
main in  the  95  per  cent,  alcohol  two  minutes  ;  thick  sections,  ten  minutes 
or  longer.*  Then  the  sections  are  transferred  for  clearing  to  a  watch- 
glass  containing  3  c.c.  of  oil  of  bergamot,  as  much  as  possible  of  the 
alcohol  being  removed  with  filter-paper  before  placing  them  in  the  clearing 
agent. f  If  the  watch-glass  is  placed  on  a  black  background  the  effect 
of  the  oil  can  be  watched,  and  it  will  be  seen  that  the  sections  gradually 
become  transparent.  Care  must  be  taken  not  to  breathe  into  the  watch- 
glass,  or  the  oil  of  bergamot  will  immediately  become  turbid.  If  some 
areas  of  the  section  do  not  become  transparent  within  two  or  three 
minutes  (such  areas  appear  white  and  opaque  in  direct  light,  black-brown 
in  transmitted  light),  this  indicates  that  the  section  is  not  dehydrated  and 
it  must  be  put  back  into  the  absolute  alcohol.  When  the  clearing  is  com- 
pleted the  section  is  transferred  to  a  dry  slide,  the  superfluous  oil  J  absorbed 
with  filter-paper  or  carefully  wiped  up  ||  with  a  linen  cloth  turned  over  the 
index-finger,  and  a  cover-glass,  from  the  under  surface  of  which  a  drop 
of  damar  is  suspended,  applied.  If  several  sections  are  to  be  mounted 
under  one  cover,  arrange  them  close  together  with  a  needle  ;  then,  by 
means  of  a  glass-rod,  apply  a  thin,  even  layer  of  damar  to  the  under 
surface  of  the  cover-glass  and  place  it  on  the  sections.  Large  air-bubbles 
are  driven  out  by  placing  a  small  drop  of  damar  at  the  edge  of  the 
cover-glass  ;  on  the  following  day  it  will  be  seen  that  the  air-bubbles 
have  retreated  from  beneath  the  cover.  Small  air-bubbles  disappear 
spontaneously  and  may  be  neglected. 

It  not  infrequently  happens  to  beginners  to  discover  that  the  damar 
becomes  turbid  and  finally  renders  the  entire  preparation,  or  parts  of  it, 

*  Beginners  are  recommended  to  transfer  the  sections  from  the  water  to  5  c.c.  of  90  per 
cent,  alcohol,  and  then  to  place  them  in  an  equal  quantity  of  95  per  cent,  alcohol. 

f  Thin  sections  may  be  transferred  from  the  95  per  cent,  alcohol  directly  on  to  the  slide, 
the  superfluous  alcohol  wiped  off,  and  a  drop  of  bergamot  oil  applied.  At  first  the  oil  will  withdraw 
from  the  section  and  must  be  led  back  with  the  needle ;  when  the  clearing  is  completed,  which 
can  be  ascertained  under  the  microscope  with  the  low  power,  as  much  as  possible  of  the  oil 
should  be  wiped  up  and  a  cover-glass  with  a  drop  of  damar  applied.  When  examining 
uncovered  sections  lying  in  oil  both  oil  and  sections  often  become  clouded  by  the  moisture 
exhaled  in  breathing ;  in  this  case  drain  off  the  clouded  oil  and  add  a  fresh  drop. 

J  The  oil  in  the  watch-glass  that  has  been  used  for  clearing  may  be  returned  to  the 
bottle. 

||  The  removal  of  the  oil  is  most  readily  accomplished  by  inclining  the  slide  and  then 
wiping  it. 


THE    PREPARATION    OF    MICROSCOPIC    SPECIMENS.  47 

untransparent.  This  is  due  to  incomplete  dehydration.  If  the  clouding 
is  slight,  which  under  the  microscope  is  seen  to  consist  of  minute  drops 
of  water,  a  gentle  warming  of  the  slide  is  often  sufficient  to  remove  it. 
In  the  case  of  much-clouded  preparations,  place  the  whole  slide  in  tur- 
pentine for  half  an  hour  ;  then  carefully  lift  off  the  cover-glass,  place  the 
section  for  two  minutes  in  turpentine,  in  order  to  dissolve  off  the  adhe- 
rent varnish,  and  then  dehydrate  in  4  c.c.  of  absolute  alcohol,  which 
should  be  changed  in  five  minutes  ;  clear  in  oil  of  bergamot  and  mount 
in  damar. 

The  damar-varnish  dries  very  slowly,  therefore  the  slides  must  not 
be  stood  on  edge,  but  be  kept  in  a  horizontal  position. 

The  series  of  processes  through  which  a  fresh  object  must  pass 
until  it  is  preserved  as  stained  sections  is  a  very  long  one.  When,  for 
example,  the  directions  in  the  Special  Technic  require  :  "  Fixation  in 
Zenker's  fluid,  hardening  in  gradually  strengthened  alcohols,  staining  of 
sections  in  carmine  and  hematoxylin,  mounting  in  damar,"  the  procedure 
is  as  follows  : 

1.  Place  the  fresh   object,  about    I    cm.  in  diameter,  in   60   c.c.  of 
Zenker's  fluid  *  for  twenty-four  hours. 

2.  Wash  in  (if  possible  running)  water  for  twenty-four  hours. 

3.  Place  in  20  c.c.  of  distilled  water  for  about  fifteen  minutes. 

4.  Transfer  to    50   c.c.    of    50  per     cent,  alcohol   for   twenty-four 
hours  ;  from  now  on   the  object  is  to  be  kept  in  the  dark  (see  p.  33, 
remark*). 

5.  Transfer    to    50  c.c.    of    70   per   cent,   alcohol   for   twenty-four 
hours. 

6.  Transfer   to  50  c.c.  of  90  per  cent,  alcohol   and  tincture  of  iodin 
for  from  eight  to  fourteen  days,  daily  adding  tincture  of  iodin  (p.  32). 

7.  Transfer   to   pure  90  per  cent,  alcohol,  which  is  to  be  changed 
two  or  three  times. 

The  object  thus  fixed  and  hardened  can  be  sectioned  at  once  or  may 
remain  indefinitely  in  the  90  per  cent,  alcohol,  which  during  this  period 
should  perhaps  be  changed  once  more.f 

8.  Transfer  the  sections  from  the  alcohol  (p.  36)  to   20  c.c.  of  dilute 
carmine  solution  for  twenty-four  hours. 

9.  Place  them  in  5  c.c.  of  distilled  water  for  ten  minutes. 
10.   Place  them  in  5  c.c.  of  hematoxylin  for  five  minutes. 

*  The  quantities  named  are  calculated  only  for  this  I  cm.  cube ;  for  several  or  for  larger 
objects  more  fixing  and  hardening  fluid  must  be  used. 

|  The  following  quantities  are  intended  for  from  three  to  six  sections  ;  for  a  larger  number 
of  sections  the  quantity  of  the  absolute  alcohol  in  particular  should  be  increased. 


HISTOLOGY. 


1  1.   Place  them  in  30  c.c.  of  distilled  water  for  from  ten  minutes  to 
two  hours. 

12.  Place  them  in  5  c.c.  of  95  per  cent,  alcohol  for  ten  minutes. 

13.  Place  them  in  3  c.c.  of  bergamot  oil  for  two  minutes. 

14.  Mount  in  damar. 


§  ii.   EXAMINATION   OF   FRESH    OBJECTS. 

I  have  placed  this  method  last  because  it  is  the  most  difficult  and 
presupposes  a  somewhat  practised  eye.  This  practice  is  most  readily 
acquired  by  previous  examination  of  prepared  (hardened,  stained,  etc.) 
objects  ;  having  once  clearly  perceived  and  studied  peculiarities  of  struct- 
ure, it  is  then  not  difficult  to  detect  them  again  in  fresh  objects,  even 
though  the  majority  of  the  details  leave  something  to  be  desired  in  point 
of  distinctness.  .  The  following  instructions  should  be  observed  : 

The  slide  and  the  cover-glass  must  not  be  oily.  They  should  be 
cleansed  with  alcohol  and  dried  with  a  perfectly  clean  cloth.*  Then 
transfer  one  drop  of  a  0.75  per  cent,  salt  solution  (p.  19)  to  a  slide, 
place  in  it  a  small  piece  of  the  object  to  be  examined  and  cover  it  with 
a  cover-glass.  Pressure  must  be  carefully  avoided  ;  if  the  structures  are 
very  delicate,  support  the  cover-glass  on  two  strips  of  thin  paper  placed 
at  the  sides  of  the  object.  If  the  object  requires  no  further  treatment, 
the  cover-glass  should  be  sealed  with  paraffin  to  prevent  evaporation. 
Melt  a  small  piece  of  paraffin  on  the  blade  of  an  old  scalpel  and  let  it  flow, 
not  from  the  tip  but  from  the  edge,  on  to  the  rim  of  the  cover-glass  ; 
gaps  that  may  occur  in  this  frame  of  paraffin  can  be  closed  with  the  re- 
heated scalpel.  In  most  cases  the  influence  of  certain  reagents  (acids, 
alkalies,  stains)  is  studied  directly  under  the  microscope.  It  is  then 
necessary  to  remove  a  portion  of  the  medium  in  which  the  object  happens 
to  be  mounted  (in  the  present  instance  the  salt  solution)  and  to  replace 
it  by  another  fluid.  For  this  purpose  place  a  drop  of  picrocarmine 
at  the  right  edge  of  the  cover-glass.  Should  the  drop  not  touch 
the  edge  of  the  cover-glass,  do  not  incline  the  slide,  but  lead  it  with 
a  needle  to  the  appropriate  position.  It  may  now  be  seen  that  a 
little  of  the  staining  fluid  mingles  with  the  salt  solution,  but  does 
not  properly  flow  under  the  cover-glass.  In  order  that  this  may 
occur,  place  at  the  left  edge  of  the  cover-glass  a  little  piece  of  filter- 


*  For  removing  the  oil  from  new  cover-glasses,  heating  them  on  a  piece  of  sheet-iron  for 
five  minutes  over  the  flame  of  a  Bunsen  burner  is  recommended. 


THE    PREPARATION    OF    MICROSCOPIC    SPECIMENS.  49 

paper  *  and  presently  the  picrocarmine  will  be  seen  to  diffuse  under  the 
cover-glass  and  occupy  the  entire  area.f  Then  remove  the  filter-paper 
and  let  the  stain  act  ;  when  the  staining  is  completed — this  can  be 
ascertained  under  the  microscope — place  at  the  right  edge  of  the  cover- 
glass  a  drop  of  diluted  glycerol  to  which,  in  picrocarmine  staining,  as 
much  acetic  acid  is  added  as  will  drop  from  a  steel  needle  (hence  a  very 
small  drop),  and  again  apply  the  filter-paper  to  the  left  edge  of  the  cover- 
glass.  In  this  way  a  whole  series  of  fluids  can  be  passed  through 
beneath  the  cover-glass,  and  their  action  on  the  tissues  studied.  Some  of 
these  fluids — for  example,  picrocarmine — must  remain  in  contact  with  the 
objects  for  a  very  long  time  if  they  have  been  previously  fixed  with  osmic 
acid.  In  this  case  evaporation  is  prevented  by  placing  the  object  in  a 
moist-chamber.  For  the  construction  of  the  moist-chamber  a  porcelain 
plate  and  a  small  bell-glass  9  cm.  in  diameter  are  required.  Pour  water 
into  the  plate,  to  the  depth  of  2  cm.  and  stand  in  the  middle  a  small 
glass-dish  ;  on  the  latter  place  the  slide  with  the  preparation  and  cover 
the  whole  with  the  glass-bell,  the  free  edge  of  which  must  be  submerged 
in  the  water. 


§    12.    STORING  OF  PERMANENT  PREPARATIONS. 

The  finished  preparations  should  be  promptly  labeled.  Labels  of 
cardboard  about  1.2  mm.  thick,  glued  to  the  slide  with  fish-glue  (isinglass) 
are  preferable  to  those  of  gummed  paper  ;  the  slides  can  then  be  placed 
one  upon  the  other  without  injury  to  the  preparations.  The  labels  should 
be  as  large  as  possible  (2  cm.  square  for  slides  of  English  form)  and 
should  bear  the  name  of  the  animal,  of  the  organ,  and  if  possible  a  brief 
statement  of  the  methods  used.  Of  the  cases  J  for  storing  the  prepara- 
tions only  such  should  be  chosen  in  which  the  slides  lie  flat,  not  those 
in  which  they  stand  on  edge. 


*  Cut  a  strip  4  cm.  long  and  2  cm.  broad,  fold  it  square  and  place  the  paper  tent  thus 
formed  on  the  slide,  so  that  one  of  the  narrow  ends,  which  must  be  perfectly  straight,  touches 
the  left  edge  of  the  cover-glass. 

f  After  the  first  drop  has  penetrated,  place  two  or  three  additional  drops  at  the  right  edge 
of  the  cover-glass. 

\  The  best  and  cheapest  cases  are  kept  by  Th.  Schroter,  Leipzig,  Windmiihlenstr.  No. 
46.  I  recommend  for  box  form,  pattern  O  (for  about  300  slides),  price  2  M.  (50  cents)  ;  for 
tray  form,  Py  with  flat  covers  for  10  to  20  slides  (according  to  size),  price  45  Pfennige 
(about  12  cents).  The  tray  form  has  the  great  advantage  of  allowing  all  the  specimens  to  be 
seen  at  once.  In  the  United  States,  Schroter's  boxes  and  trays  are  supplied  by  King  &  Co., 
New  York,  and  other  dealers. 


III.   MANAGEMENT  OF  THE  MICROSCOPE. 

In  conformity  with  the  position  taken  in  the  introduction,  an  exhaus- 
tive description  of  the  optic  and  mechanical  parts  of  the  microscope 
cannot  be  entered  upon  here.  Fig.  I  will  recall  to  the  reader  the  usual 
names  of  the  several  parts  of  the  microscope. 

The  first  requisite  in  the  use  of  the  microscope  is  perfect  cleanliness 
of  all  its  parts  (see  also  p.  17).  The  surface  of  the  mirrors,  objectives, 
and  oculars  should  not  be  touched  with  the  fingers.  The  objective 
should  be  held  with  the  lower  end  directed  toward  the  window  and 
the  clearness  of  the  reflected  image  thus  tested.  Foreign  matter  on  the 
ocular  can  be  detected  by  rotating  the  latter  in  the  tube,  when  anything 
that  is  adherent  will  revolve. 

After  the  ocular  has  been  placed  in  the  upper  end  of  the  draw-tube 
and  a  low-power  objective  screwed  on  the  lower  end  of  the  tube  (or  on 
the  revolver,  if  used),  the  field  of  view  of  the  microscope  should  be  illu- 
minated with  light  reflected  from  a  suitable  source  by  the  concave  mirror 
placed  below  the  stage.  This  is  best  accomplished  by  moving  the  mirror 
tentatively  in  all  directions  (with  the  diaphragm  widely  open,  and  the 
front-lens  of  the  objective  about  I  cm.  above  the  level  of  the  stage)  till 
the  eye,  looking  simultaneously  through  the  eye-piece  into  the  micro- 
scope, sees  the  field  of  view  brightly  and  uniformly  illuminated.*  The 
concave  mirror  should  be  used  with  dry  lenses,  except  when  a  substage 
condenser  is  employed. 

The  light  reflected  from  a  white  cloud  or  from  a  white  window-blind 
illuminated  by  the  sun  is  recommended  ;  less  desirable  but  still  useful  as 
a  source  of  light  is  the  blue  sky.  Direct  sunlight  must  be  avoided.  In 
using  artificial  illumination  the  light  should  be  taken  from  the  inner  sur- 
face of  a  white  lamp-shade,  not  directly  from  the  flame.  A  screen  of  blue 

*  The  rays  of  light  reflected  from  the  mirror  in  this  position  pass  perpendicularly  through 
the  object  on  the  stage.  This  is  called  "  central  illumination. "  For  distinguishing  slight  dif- 
ferences of  level  between  adjacent  parts  of  an  object  it  is  of  advantage  to  use  "  oblique  or  lateral 
illumination"  to  obtain  which  the  mirror  is  moved  to  the  side  so  that  the  rays  reflected  from  it 
strike  the  object  obliquely.  When  lateral  illumination  is  used  the  diaphragm  and  the  cylinder 
in  which  it  is  mounted  must  be  removed,  so  that  the  opening  in  the  stage  shall  be  as  large  as 
possible. 

50 


MANAGEMENT    OF    THE    MICROSCOPE.  5  I 

•  Eye-piece  (Ocular) 


Tube 


Triple  revolver 
Objective  •   •   • 


•  Draw-tube 


Rack  and  pinion  adjustment 


•  Micrometer  Screw 


FIG.  i.— LEITZ  MICROSCOPE.    STAND  II  (y2  actual  size). 

glass  placed  between  the  mirror  and  the  source  of  light,  or  between  the 
mirror  and  the  object,  agreeably  subdues  artificial  light,  without  essen- 
tially injuring  the  definition  of  the  image.  It  is  obvious  that  the  micro- 


5  2  HISTOLOGY. 

scopist  should  not  sit  in  direct  sunlight  ;  the  instrument  should  be  placed 
about  a  meter  from  the  window. 

Having  secured  the  light  the  examination  may  begin.  Ahvays  ex- 
amine first  with  the  low-power,  then  with  the  high-power  objective  ;  do  not 
use  strong  oculars,  they  narrow  and  darken  the  field  of  view  and  render 
the  examination  much  more  difficult*  The  low-  and  the  medium-power 
oculars  (Leitz,  Oc.  I)  of  the  usual  outfit  supplied  with  the  microscope 
answer  for  the  great  majority  of  cases. 

The  increased  magnification  obtained  by  drawing  out  the  draw-tube 
is  seldom  necessary.  With  low-power  lenses  a  diaphragm  having  a  large 
opening  should  be  used  ;  with  high-power  lenses,  a  diaphragm  having  a 
small  opening.  In  focusing  the  object,  the  coarse  adjustment  by  rack 
and  pinion  is  used  first  ;  the  objective  is  placed  near  to  the  object,  but  at 
a  distance  greater  than  its  focal  length,  and  then,  with  the  eye  applied  to 
the  ocular,  the  tube  should  be  gradually  lowered  until  the  indistinct  out- 
lines of  the  image  appear,  which  is  then  brought  into  distinct  view  by 
means  of  the  fine  adjustment  or  micrometer-screw.  The  left  hand  should 
hold  the  slide,  while  the  right  should  remain  at  the  micrometer-screw. 
Since  only  the  points  lying  in  a  single  plane  of  the  object  can  be  in  focus 
and  distinctly  seen  at  one  time,  the  preparation  must  be  examined  with 
slight  raising  and  lowering  of  the  tube,  that  is,  with  change  of  focus  by 
gently  turning  the  micrometer-screw.  In  using  the  microscope  the  habit 
should  be  formed  of  keeping  both  eyes  open. 

One  should  never  neglect  to  examine  the  preparations  with  a  hand- 
lens.  For  this  purpose  the  oculars  (e.g.,  Leitz,  Oc.  Ill)  can  be  used. 
The  mounted  specimen  is  held  with  the  cover-glass  side  toward  the 
light ;  the  upper  or  back-lens  of  the  ocular  is  placed  directly  against  the 
slide,  the  eye  applied  to  the  lower  or  front-lens. 


DRAWING. 

An  invaluable  aid  to  study  is  the  drawing  of  the  microscopic  object. 
The  power  of  observation  is  made  considerably  keener,  and  many 
details  which  would  be  otherwise  completely  overlooked  are  discovered 
while  the  sketch  is  in  progress.  Even  the  most  attentive  examination 
cannot  replace  the  advantage  which  drawing  yields.  Those  who  have 
little  practice  in  drawing  should  nevertheless  try  to  sketch  the  prepara- 
tions under  both  low-  and  high-power  objectives.  For  this  purpose  the 


*  The  majority  of  the   preparations  from  which  the  illustrations  in  this  book  were  taken 
were  examined  and  sketched  with  weak  oculars. 


MANAGEMENT    OF    THE    MICROSCOPE.  53 

drawing-paper  should  be  on  a  level  with  the  stage,  the  left  eye  applied 
to  the  microscope,  the  right  eye  directed  to  the  paper  and  the  pencil-point. 
At  first  this  is  somewhat  difficult,  but  a  little  practice  will  soon  give  the 
necessary  facility. 

MEASUREMENT. 

For  this  purpose  an  ocular-micrometer  and  a  stage-micrometer  are 
used.* 

The  latter  is  laid  on  the  stage  of  a  microscope  provided  with  an 
ocular-micrometer,  and  the  number  of  divisions  of  the  ocular-micrometer 
which  corresponds  to  one  part  of  the  stage-micrometer  is  counted,  f 
The  dimensions  of  the  spaces  of  the  stage-micrometer  being  known,  the 
size  of  the  object,  which  with  a  given  magnification  will  occupy  one  or 
more  of  the  divisions  of  the  ocular-micrometer,  is  easily  calculated. 
The  following  illustrations  may  render  the  manipulations  intelligible  : 

Ocular  I,  and  draw-tube  pushed  in,  5  divisions  of  the  ocular-micro- 
meter correspond  with  I  division  of  the  stage-micrometer.  Each  division 
of  the  stage-micrometer  used  =  -^  mm.  Hence  5  divisions  of  the 
ocular-micrometer  =  ^V  (0.05  mm.),  and  I  division  of  the  ocular- 
micrometer  =  o.oi  mm.  If,  then,  any  microscopic  object,  e.  g.t  a 
striated  muscle-fiber,  the  diameter  of  which  is  to  be  measured  with  this 
magnification,  occupies  4  divisions,  the  fiber  is  0.04  mm.  broad. 

It  is  often  difficult,  especially  with  low  magnification,  to  count  the 
fine  divisions  of  the  ocular-micrometer.  This  can  be  more  easily  done, 
by  noting  the  longer  lines  marking  every  fifth  or  tenth  division.  For 
instance,  with  Leitz  Objective  3,  Ocular  I,  and  the  draw-tube  drawn  out, 
40  divisions  of  the  ocular-micrometer  correspond  with  5  divisions  of  the 
stage-micrometer.  Therefore,  40  divisions  =  -f^  mm.  =  0.25  mm., 
and  i  division  of  the  ocular-micrometer  with  this  magnification  = 
0.0062  mm.,  2  divisions  =  0.0124  mm.,  and  so  on. 

With  Leitz  Objective  7,  Ocular  I,  and  draw-tube  pushed  in,  30  divis- 
ions of  the  ocular-micrometer  correspond  with  I  division  of  the  stage - 


*  Some  ocular-micrometers  (Leitz)  are  made  to  rest  upon  the  diaphragm  inside  the  ocular; 
others  (Seibert)  to  be  inserted  through  a  lateral  opening ;  or,  in  some  cases,  special  oculars 
(Zeiss)  for  measuring  are  made  for  the  microscope.  The  actual  size  of  the  divisions  of  the 
ocular-micrometer  need  not  be  known.  The  stage-micrometer  is  a  glass  slide  on  which  I  mm. 
with  loo  subdivisions  is  engraved.  Instead  of  this  a  second  ocular-micrometer,  which  usually 
contains  a  mm.  with  only  20  divisions,  may  be  used.  Measurements  made  with  this  are  not 
so  accurate,  but  the  errors  are  so  insignificant  that  they  scarcely  need  consideration. 

f  Beginners  often  find  it  difficult  to  focus  the  lines  on  the  stage-micrometer ;  faint  or 
oblique  illumination  of  the  object  makes  it  easier  to  detect  the  lines. 


54  HISTOLOGY. 

micrometer;  30  divisions  =  0.05  mm.,  I  division  —0.0017  mm.,  or  17  <>. 
Finally,  with  Leitz  Objective  7,  Ocular  I,  and  draw-tube  drawn  out,  40 
divisions  of  the  ocular-micrometer  =  I  division  of  the  stage-micrometer. 
Therefore,  40  divisions  =  0.05  mm.,  I  division  =  0.0012  mm.,  or 
12  P. 

It  is  advisable,  if  one  has  many  microscopic  measurements  to  make, 
to  prepare  a  table  for  each  magnification  used,  in  which  the  equivalent 
values  of  i,  2,  3  .  .  .  .  20,  30,  40  .  .  .  .  100  scale  divis- 
ions of  the  ocular-micrometer  are  given.  It  must  be  emphasized  that  the 
foregoing  calculations  by  no  means  apply  to  all  the  microscopes  made  by 
Leitz.  The  values  must  be  specially  determined  for  every  instrument  by 
the  above-given  method. 

In  conclusion,  the  microscopist  is  advised  to  be  patient,  very  patient  ; 
if  his  preparations  are  unsuccessful,  let  him  not  search  for  the  cause  in  the 
deficiency  of  the  methods  recommended — I  have  often  tested  them — but 
in  himself;  he  who  cannot  accustom  himself  to  conscientiously  follow  the 
written  instructions,*  who  grasps  delicate  objects  with  his  fingers,  who 
contaminates  the  reagents  by  pouring  one  into  the  other,  who  leaves 
objects  in  fixing  fluids  exposed  to  the  sun  or  allows  them  to  become  dry, 
has  not  the  right  to  expect  good  results  from  his  slovenly  work. 

*  The  periods  of  time  given  for  staining,  dehydrating,  etc.,  have  only  an  approximate 
value.  They  vary  within  considerable  limits  in  accordance  with  the  thickness  of  the  sections, 
the  concentration  of  the  solutions,  etc.  Experience  will  soon  teach  the  microscopist  to  deter- 
mine the  precise  period  of  time. 


PART    II. 
MICROSCOPIC  ANATOMY  AND   SPECIAL  TECHNIC. 

The  animal  body  consists  of  cells  which  are  derived  from  a  single 
cell  by  repeated  division.  At  the  beginning  of  development  the  cells  are 
of  similar  form,  all  are  spherical  structures,  and  none  is  furnished  with 
special  characteristics  that  distinguish  it  from  its  companions.  The  cells 
are  still  undifferentiated.  In  the  course  of  development  the  cells  arrange 
themselves  in  flat,  superposed  layers,  the  germ-layers.  With  the  sepa- 
ration in  germ-layers  and  the  formation  of  organs  from  these,  the  cells 
cease  to  resemble  one  another,  they  become  differentiated.  As  a  rule, 
the  cells  that  have  developed  in  the  same  direction  are  united  in  com- 
plexes, without  definite  spatial  limitation,  and  thus  form  a  tissue. 
A  tissue,  therefore,  is  a  complex  of  similarly  differentiated  cells.  We  dis- 
tinguish four  principal  tissues  :  i,  the  epithelial  tissues  ;  2,  the  supporting 
tissues  ;  3,  the  muscular  tissues  ;  4,  the  nervous  tissues.  So  long  as  these 
tissues  are  still  young  they  consist  only  of  similar  elements,  of  cells  ; 
but  in  the  course  of  development  this  condition  is  changed  in  a  twofold 
manner.  First,  the  cells  produce  special  substances,  which,  being  de- 
posited between  them,  are  called  intercellular  substances.  By  this  pro- 
cess, however,  the  character  of  the  tissue  is  not  essentially  altered.  The 
definition  of  tissue  given  above  need  be  only  so  far  extended  that  we  call 
a  tissue  a  complex  of  similarly  differentiated  cells  and  their  derivatives. 
More  radical  is  the  second  change,  consisting  in  the  penetration  of  a 
tissue  of  one  kind  by  other  tissues.  The  extent  of  this  change  varies 
greatly  in  different  cases.  It  is  least  marked  in  the  case  of  the  epithelial 
tissues,  more  so  in  the  supporting  tissues.  Muscular  and  nervous  tissues 
in  their  developed  forms  are  mixed  with  other  tissues  to  such  a  degree 
that  even  though  among  the  differentiated  elements  muscle  and  nerve 
predominate,  in  the  sense  of  the  given  definition  they  can  scarcely  be 
called  tissues.*  The  tissues,  therefore,  are  not  equivalent  among  them- 

*  For  this  reason  the  proposition  has  been  made  to  omit  a  division  of  tissues  and  to  dis- 
tinguish only  elements  and  organs. 

55 


56  HISTOLOGY. 

selves  ;  in  the  lowest  rank  stand  the  epithelial  tissues  and  the  supporting 
tissues  ;  both,  though  differing  from  each  other  in  form  and  function, 
occur  also  in  the  plant-world  ;  we  can  therefore  class  them  as  vegetative 
tissues.  On  a  higher  level,  as  well  morphologically  as  physiologically, 
stand  the  muscular  and  nervous  tissues,  that,  being  found  only  in  the 
animal  body,  are  called  animal  tissues. 

When  different  tissues  unite  in  the  formation  of  a  body  of  definite 
internal  structure  and  definite  external  form,*  they  constitute  an  organ. 

Accordingly  our  task  resolves  itself  into  :  I,  the  study  of  the  cells 
and  of  the  tissues,  and,  2,  the  study  of  the  organs.  The  investigation 
of  cells  and  of  tissues  is  the  object  of  histology.  Histology  is  a  part  of 
general  anatomy,  which,  because  of  the  instrument  most  used  in  its 
study,  is  called  microscopic  anatomy.  The  investigation  of  organs,  also, 
so  far  as  it  can  be  done  with  the  aid  of  the  microscope,  is  the  task  of 
microscopic  anatomy. 


I.  HISTOLOGY. 

{Microscopic  Anatomy  of  Cells  and  Tissues.) 

A.    CELLS. 

A  cell,  cellula,  is  a  spatially-limited  structural  element,  which  under 
certain  conditions  is  able  to  nourish  itself,  to  grow,  and  to  multiply.  In 
virtue  of  these  properties  the  cell  is  called  an  elementary  organism. 

The  essential  parts  of  a  cell  are:  i.  The  protoplasm,  or  cell-body, 
a  soft,  semi-fluid  substance  of  alkaline  reaction,  insoluble  in  water,  highly 
distensible,  that  consists  principally  of  albuminous  substances,  much 
water,  and  salts,  and  contains  a  special  nitrogenous  proteid,  plastin.  In 
the  protoplasm  small  granules,  microsomes,  occur  in  variable  quantity ; 
when  numerous  they  may  give  to  the  protoplasm  a  darker  appearance. 
They  are  irregularly  distributed,  namely,  are  absent  in  the  superficial 
layer,  the  exoplasm,  which  is  somewhat  denser  and  perhaps  possesses  a 
special  function.  With  the  aid  of  very  high  magnifying  powers  it  is  seen 
that  protoplasm  possesses  structure  :  a  reticulum,  spongioplasm,  which  is 


*  Usually  in  the  definition  of  an  organ  "  the  definite  function  "  is  included  ;  but  this  does 
not  come  within  the  limits  of  a  morphologic  definition,  nor  is  it  a  special  peculiarity  of  an  organ, 
but  may  be  the  property  of  a  cell  as  well  as  of  a  tissue. 


CELLS. 


57 


embedded  in  an  amorphous  ground-substance,  liyaloplasm  (Flemming).* 
2.  The  nucleus,  a  clear,  sharply-defined,  usually  vesicular  body  lying  in 
the  middle  of  the  cell,  that  consists  of  several  proteid  substances,  chro- 
matin, or  nuclein,/j;r;//;/,  or  paranuclein,  linin,  "  nuclear  fluid,"  or  matrix, 
and  amphipyrenin.  Chromatin  and  pyrenin,  by  their  affinity  for  stains,  are 
distinguished  from  the  other  three  so-called  achromatin  substances,  but 
differ  chemically  from  each  other.  For  example,  on  the  addition  of  dis- 
tilled water  the  structures  composed  of  chromatin  disappear,  while  those 
composed  of  pyrenin  remain  intact.  In  the  simplest  case  (in  spermatozoa), 
the  nucleus  is  a  compact  mass  of  chromatin,  to  which  the  pyrenin  is 
attached,  but  usually  it  consists  of  a  network  of  fine  linin-threads  and 
coarser  chromatin-cords.  f  The  chromatin-cords  are  of  different  caliber, 
and  at  intervals  exhibit  isolated  enlargements  ("  net-knots,"  karyosomes), 


Nuclear  membrane. 


Lini 


Nuclear  fluid  (matrix).    -.«,. 


Nucleolus. 


Chromatin-cords  (nuclear 
network). 


Nodal  enlargements  of     .-'' 
the  chromatin. 


Cell-membrane. 


Exoplasm. 


Microsomes. 


Centrosome. 


I---H--  « 

•{"(  s  y^V/r  7 Spongioplasm. 

•£$$£/ 

Hyaloplasm. 


r-:^—  -    Foreign  enclosures. 
FIG.  2. — DIAGRAM  OF  A  CELL.     Microsomes  and  spongioplasm  are  only  partly  drawn. 


that  must  not  be  confused  with  the  nucleoli.  Linin  and  chromatin  form 
the  nuclear  network,  the  interstices  of  which  are  occupied  by  one  or  more 
nucleoli  consisting  of  pyrenin  and  by  the  nuclear  fluid.  $  The  nuclear 

*  The  theories  concerning  the  structure  of  protoplasm  are  by  no  means  agreed.  Accord- 
ing to  Fromann,  Leydig,  and  others,  protoplasm  is  a  spongy  structure,  that  is,  it  consists  of  a 
network,  the  meshes  of  which  contain  a  fluid.  According  to  Butschli,  the  structure  is  froth-like, 
that  is,  it  contains  small  spaces  that  do  not  communicate  with  one  another.  According  to  the 
much-disputed  theory  of  Altmann,  protoplasm  is  composed  of  granules  (granula,  bioplasts), 
connected  by  an  indifferent  substance,  and  these  are  the  real  elementary  organisms. 

f  In  suitable  preparations  it  may  be  seen  that  the  chromatin-cords  are  composed  of 
rows  of  granules  which  lie  in  contact  with  threads  of  linin.  This  is  shown  in  the  upper  half 
of  the  diagram  (Fig.  2). 

J  Recently  a  special  structure  has  been  ascribed  to  the  nuclear-sap ;  it  is  said  to  consist 
of  a  substance  in  the  form  of  a  framework,  within  which  are  a  fluid  and  tumescent  granules. 


58  HISTOLOGY. 

membrane,  not  always  present,  is  composed  of  amphipyrenin  ;  often  a 
membrane  is  simulated  by  a  thin  superficial  layer  of  chromatin.  The 
nuclear  network  and  the  nucleoli  undergo  important  changes  according  to 
the  age  of  the  cell.  3.  The  centrosome,  a  usually  diminutive  corpuscle 
within  the  nucleus,  from  which  fine  threads  extend  to  the  chromatin- 
cords  and  to  the  nuclear  membrane.  Because  of  its  minuteness  it  can 
be  seen  only  in  particularly  favorable  objects  (in  the  spermatocytes  of 
Ascaris  megalocephala  univalens,  in  carcinoma  cells) ;  it  becomes  more 
distinct  when  it  wanders  from  the  nucleus  into  the  protoplasm,  which 
it  does  during  the  division  of  the  cell.  In  the  protoplasm  the  cen- 
trosome seems  to  be  able  to  remain  for  a  considerable  period  and  there 
it  was  first  discovered  (Fig.  3). 

Most  cells  contain  but  one  nucleus  ;  only  a  few  have  several  nuclei 
(some  wandering-cells,  giant-cells,  and  others).  Non-nucleated  cells 
(horny  cells  of  the  epidermis,  colored  blood-corpuscles  of  mammals) 
originally  possess  nuclei,  but  lose  them  in  the  course  of  development. 

An  unessential  element  of  the  cell 
is  the  cell-membrane,  which  is  wanting  in 
many  cells  and  when  present  is  either  a 
transformation  of  the  peripheral  zone  of 
the  protoplasm  or    a  secretory  product 
•  Centrosome.       of    t}ie    Jatter ;     it     appears    as    a    thin, 
FIG.  3.— CELL  OF  THE  BONE-MARROW  OF      usually    structureless     envelope.        The 

A  RABBIT.     X  1500.    The  double  centro- 
some lies  in  a  clear  area,  the  attraction-       protoplasm  of  cells    may  contain   adven- 
sphere. 

titious  materials,  pigment,  glycogen,  etc., 

and  globules  of  fat,  of  aqueous  and  slimy  fluids.  The  term  paranucleus 
has  been  used  to  designate  various  structures,  the  significance  of 
which  is  not  yet  in  each  case  determined.  A  paranucleus  is  often 
simulated  by  the  remnants  of  degenerated  cells  that  have  been  in- 
corporated in  a  living  cell.  In  other  cases  the  paranucleus  is  confused 
with  the  centrosome. 

Cells  differ  greatly  in  forrru  They  may.  be  :  spherical,  the  typical 
form  of  all  cells  in  the  embryonal  period,  and  in  the  adult,  for  example, 
resting  leucocytes  are  spherical  ;  discoid,  e.  g.,  the  colored  blood-cor- 
puscles ;  polyhedral,  e.  g.,  the  liver-cells  ;  cylindrical  or  columnar,  e.  g., 
the  epithelium  of  the  small  intestine  ;  cubical,  e.  g.,  the  epithelium  of  the 
capsule  of  the  crystalline  lens  ;  flattened  (so-called  squamous  epithelium), 
e.  g.,  the  epithelial-cells  of  the  blood-vessels  ;  spindle-shaped,  e.  g.,  many 
connective-tissue  cells  ;  elongated  into  fibers,  e.  g.,  smooth  muscle-fibers  ; 
and  stellate,  e.  g.,  many  ganglion-cells.  The  form  of  the  nucleus  usually 
corresponds  to  the  form  of  the  cell.  It  is  more  or  less  oval  in  columnar, 


CELLS.  59 

spindle,  and  stellate  cells  ;  rounded  in  spherical  and  cubical  cells.  Lobu- 
lated,  so-called  polymorphous,  nuclei  are  found  in  leucocytes  and  in 
giant-cells  ;  they  are  a  symptom  of  activity  on  the  part  of  the  cell,  tending 
either  to  locomotion  or  change  in  form,  or  to  increased  metabolic  energy. 

The  size  of  cells  varies  from  forms  microscopically  small,  47** 
(colored  blood-corpuscles),  to  macroscopic  bodies  (eggs  of  birds,  of  am- 
phibians). The  size  of  the  nucleus  corresponds  in  general  to  that  of  the 
protoplasmic  body ;  only  mature  ova,  despite  their  great  dimensions, 
have  minute  nuclei. 

The  vital  properties  of  cells  will  be  discussed  here  only  in  so  far  as 
they  can  be  studied  by  direct  microscopic  observation  ;  other  details 
must  be  sought  in  text-books  of  physiology.  Accordingly,  the  phe- 
nomena of  motion  in  cells,  the  reproduction  of  cells,  and  those  micro- 
scopic processes  which  are  associated  with  the  secretory  activity  of  cells 
will  be  considered. 


3/y  5  II  H  ill  Minutes. 

FIG.  4.— LKUCOCYTKS  OK  A  FROG.  X  560.    Changes  in  form  observed  during  ten  minutes.  Techn.  No.  43. 


phenomena  of  motion  occur  in  the  form  of  ameboid  f  activity,  of 
ciliary  motion,  and  of  contraction  of  certain  fibers  (muscle-fibers).  The 
ameboid  movement  is  the  most  important  ;  it  has  been  observed  in 
nearly  all  the  cells  of  the  animal  body.  In  well-marked  cases,  e.  g.,  in 
leucocytes,  the  protoplasm  of  the  cells  throws  out  finer  or  coarser 
processes  (pseudopodia),  which  by  dividing  and  flowing  together  produce 
a  great  variety  of  forms.  These  processes  may  be  retracted  or  they 
may  become  fixed  and  draw  the  remainder  of  the  cell-body  after  them, 
the  result  of  which  is  locomotion,  or  the  so-called  "  wandering"  of  cells. 
The  wandering-cells  play  an  important  part  in  the  economy  of  the  animal 
body.  The  processes  can  flow  around  and  enclose  foreign  particles  or 
small  cells,  an  incident  described  as  the  feeding  of  the  cell.  J  Ameboid 

*  A  mikron,  fitKpov  =  //  =  o.ooi  mm. 

f  This  movement  is  exhibited  in  its  perfection  by  unicellular  organisms  named  amebse, — 
thence  the  phrase  "  ameboid  movement." 

J  This  must  not  be  confused  with  the  nutrition  of  the  cell,  which  is  effected  by  a  series  of 
complicated  chemical  processes  within  the  cell  :  diosmotic  currents,  imbibition,  molecular  pres- 
sure, etc. 


6O  HISTOLOGY. 

movements  ensue  very  slowly  ;  in  warm-blooded  animals,  only  on  arti- 
ficial warming  of  the  object.  For  ciliary  motion  and  contraction  see  the 
Epithelial  Tissues  and  the  Muscular  Tissues. 

There  is  still  another  movement  that  is  observed  not  only  in  the 
living  but  also  in  the  dead  cell.  This  is  the  so-called  molecular  motion, 
an  oscillation  of  minute  granules  in  the  cell,  the  result  of  molecular 
currents  in  the  fluid  in  which  they  are  suspended.  It  may  often  be 
observed  in  the  salivary  corpuscles  (see  the  Lymph-follicles  of  the 
Tongue). 

Reproduction  and  Multiplication  of  Cells. — Formerly,  two  kinds  of 
cell-formation  were  distinguished, — spontaneous  generation  (generatio 
(zquivoca)  and  generation  by  division.  According  to  the  theory  of 
spontaneous  generation,  cells  originated  in  a  suitable  fluid,  cytoblastema. 
This  view  has  been  utterly  abandoned.  Only  one  kind  of  cell-generation 
is  now  recognized  ;  namely,  reproduction  by  division  of  preexisting  cells, 
"  Omnis  cellula  e  cellula."  * 

In  the  division  of  a  cell,  first  the  nucleus  and  then  the  protoplasm 
divides  into  two  usually  equal  parts.  In  this  process  a  special  grouping 
and  rearranging  of  the  nuclear  substances  take  place  according  to 
definite  laws.  This  mode  of  division  is  called  indirect  division,  mitosis,^ 
karyokinesis.  Its  cycle  is  usually  divided  into  three  phases,  as  follows  : 

(i)  Prophase. — The  centrosome  increases  in  size  and  migrates 
from  the  nucleus  into  the  protoplasm.  There  it  lies  close  beside  the 
nuclear  membrane,  surrounded  by  a  clear  zone  from  which  delicate 
threads  radiate,  that  collectively  are  called  astrosphere,  or  attraction- 
sphere.  The  centrosome  now  divides  in  halves,  each  of  which  is  sur- 
rounded by  an  attraction-sphere.  Then  the  nucleus  enlarges ;  the 
nuclear  network  becomes  richer  in  chromatin  and  the  chromatin-cords 
assume  the  form  of  tortuous  segments,  chromosomes,  J  transversely  dis- 

*  Likewise,  a  new  nucleus  can  be  formed  only  by  the  division  of  an  existing  nucleus. 
The  theory  of  spontaneous  generation  of  nuclei,  according  to  which  nuclei  originate  directly  from 
the  protoplasm  and  independently  of  existing  nuclei,  lacks  convincing  evidence. 

f  Mtrof  =  thread,  because  in  this  process  threads  are  visible  in  the  nucleus.  There  is 
a  second  mode  of  division,  in  which  the  nuclei  divide  simply  by  constriction,  without  a  definite 
grouping  of  the  nuclear  substances.  This  is  called  direct  or  amitotic  division.  It  is,  however, 
very  probable  that  this  kind  of  division  in  vertebrates  has  not  the  significance  of  a  physiological 
multiplication  of  cells,  but  occurs  only  in  those  cells  which  are  on  the  point  of  disintegrating, 
for  very  often  the  division  of  the  protoplasm  does  not  follow,  so  that  only  a  multiplication  of 
nuclei  takes  place.  This  frequently  happens  in  leucocytes,  also  in  epithelial-cells,  e.g.,  in  the 
superficial  epithelial-cells  of  the  bladder  of  young  animals. 

J  These  segments  are  also  present  in  many  resting  nuclei,  but  are  not  easy  to  distinguish 
because  of  the  many  lateral  branches  by  which*  they  anastomose  with  their  fellows  to  form  a 


CELLS. 


6l 


posed  to  the  longitudinal  axis  of  the  nucleus,  the  number  of  which  is 
constant  for  each  animal  species.  The  form  of  these  segments  is  usually 
that  of  a  V-shaped  loop.  The  apices  or  closed  ends  of  the  loops  are 
directed  toward  a  common  center,  the  polar-field — the  area  in  which  the 
centrosomes  are  situated — their  free  ends  toward  the  opposite  pole  of  the 
cell.  This  arrangement  of  the  segments  is  called  the  close  skein.  It  is 
followed  by  a  further  thickening  of  the  segments  and  the  formation  of  the 


Close  Skein 
(viewed  from 
the  side). 
Polar-field. 


Loose  Skein  (viewed 

from  above,  /  e.,  from 

the  pole). 


Mother  Stars  (viewed  from  the  side). 


Mother  Star  (viewed        Daughter  Star.          Beginning.  Completed, 

from  above).  Division  of  the  Protoplasm. 

FIG.  5.— KARYOKINETIC  FIGURES  OBSERVED  IN  THE  EPITHELIUM  OF  THE  ORAL  CAVITY  OF  A  SALA- 
MANDER. The  picture  in  the  upper  right-hand  corner  is  from  a  section  through  a  dividing  egg  ot 
Siredon  pisciformis.  Neither  the  centrosomes  nor  the  first  stages  of  the  development  of  the  spindle 
can  be  seen  by  this  magnification.  X  560.  Techn.  No.  i  b. 

loose  skein,  in  which  the  loops  are  less  tortuous  and  some  have  their 
closed  ends  turned  away  from  the  polar-field. 

Meanwhile  the  two  centrosomes  move  apart  and  wander  along 
the  nuclear  membrane,  each  through  an  arc  of  90°.  The  interval 
between  them  is  spanned  by  delicate  fibrils,  which  form  the  "  central - 
spindle  "  ;  to  these  the  linin-filaments,  extending  from  the  centrosomes 
to  the  chromosomes  (or  chromatin-cords),  become  applied  (see  p.  57). 
Toward  the  completion  of  the  prophase  the  nuclear  membrane  vanishes 
and  the  nucleolus  becomes  invisible. 

(2)  Metaphase. — The    centrosomes    have    reached    diametrically 


network.  When  the  process  of  division  begins  the  lateral  twigs  are  retracted,  and  consequently 
the  segments  become  thicker  and  more  conspicuous.  In  some  nuclei  the  chromatin  appears  as 
a  single  filament,  which  subsequently  divides  into  chromosomes.  . 


62  HISTOLOGY. 

opposite  points  *  and  the  threads  extending  from  them  to  the  chromo- 
somes, with  which  parts  of  the  nuclear  membrane  may  be  associated, 
now  appear  in  the  figure  of  a  spindle,  the  nuclear-spindle.  At  each  apex 
of  the  spindle  is  a  centrosome  surrounded  by  an  attraction-sphere,  which 
in  this  stage  is  also  known  as  "polar-radiation."  f  The  chromatin-loops 
move  to  the  equator  of  the  spindle,  in  the  future  plane  of  division  of  the 
nucleus,  and  arrange  themselves  so  that  their  closed  ends  are  directed 
toward  the  axis  of  the  spindle,  their  free  ends  toward  the  equator. 
Viewed  from  the  apex  of  the  spindle  this  grouping  of  the  segments  has 
the  appearance  of  a  star,  mother-star  (monaster). 

During  the  formation  of  the  mother-star,  often  earlier,  in  the  first 
stages  of  the  prophase,  the  chromatin-loops  divide  longitudinally,  and 
each  forms  two  "sister-loops."  Division  of  the  nucleus  exactly  into 
halves  now  follows,  as  a  result  of  the  contraction  of  the  threads  of  the 
spindle,  by  which  one  sister-loop  of  a  pair  is  drawn  to  one  pole,  the 
other  to  the  opposite  pole  of  the  spindle.  This  process  is  called 
metakinesis.  In  this  stage  the  nuclear  segments  appear  in  the  form  of 
two  daughter-stars  (diaster). 

(3)  Anaphase. — These  figures  are  soon  obliterated.  The  lateral 
twigs  of  the  chromosomes  reappear,  anastomose  with  one  another,  and 
reproduce  the  reticulum  of  the  resting  nucleus.  Meanwhile  the  spindle 
and  the  greater  portion  of  the  polar-radiation  have  become  invisible,  the 
nuclear  membrane  is  reformed,  the  nucleus  reabsorbs  the  nuclear  fluid, 
swells  and  becomes  spherical,  and  the  nucleolus  reappears.  At  the  same 
time  the  hitherto  quiescent  protoplasm  begins  to  divide,  a  furrow  appear- 
ing at  the  equator  of  the  cell  and  deepening  until  the  separation  into 
halves  is  accomplished. 

In  rare  cases  of  mitotic  division,  especially  in  those  of  a  pathologic 
nature,  the  nucleus  simultaneously  divides  into  more  than  two. 

The  duration  of  cell-division  varies  from  a  half  hour  (in  man)  J  to 
five  hours  (in  amphibians). 

Special  modifications  of  cell-division  are  the  so-called  endogenous 
cell-formation  and  budding.  The  former  occurs  in  those  cells  which  are 
enclosed  in  a  firm  envelope  (eggs,  cartilage-cells),  and  the  mode  of 


*The  above  description  of  the  behavior  of  the  centrosomes  does  not  always  hold  good. 
For  example,  the  centrosome  in  Ascaris  megalocephala  univalens  divides  within  the  nucleus, 
which  elongates  and  extrudes  a  centrosome  at  each  end..  During  their  extrusion  the  nuclear 
spindle  is  formed.  In  succeeding  events  the  processes  are  identical. 

|  Remains  of  the  central-spindle  still  lie  in  the  axis  of  the  nuclear-spindle. 

\  The  disappearance  of  the  mitotic  figures  in  the  human  cadaver  is  not  complete  until  after 
an  elapse  of  forty-eight  hours. 


CELLS.  63 

division  is  precisely  the  same  as  that  described  above,  only  that  all  the 
descendants  of  the  mother-cell  remain  enclosed  in  the  common  capsule. 
Gemmation  or  budding  indicates  a  kind  of  unequal  cell-division,  in  which 
protoplasmic  processes  of  the  cell  are  set  free  by  constriction  and  become 
independent  cells  (see  bone-marrow). 

The  young  cells  always  resemble  in  character  the  mother-cells. 
Such  a  case  as  a  connective-tissue  cell  arising  from  the  division  of  an 
epithelial-cell  never  occurs. 

The  Phenomena  of  Secretion. — See  Secretory  Activity  of  Epithelial 
Tissue. 

The  length  of  life  of  all  cells  is  limited.  The  old  elements  disin- 
tegrate, new  ones  appear  in  their  places.  Formerly  these  phenomena 
were  not  distinguished  from  secretory  processes,  and  the  erroneous  idea 
was  entertained  that  the  process  of  secretion  terminated  in  the  death  of 
the  cell.  Dying  cells  are  characterized  by  decrease  in  the  volume  of 
both  nucleus  and  protoplasm.  The  latter  often  presents  a  notched  edge 
or  stains  deeply,  while  the  chromatin  substance  of  the  nucleus  decreases 
or  appears  in  the  form  of  irregular  fragments  that  stain  uniformly. 
Vacuolization  of  the  protoplasm  or  the  nucleus  is  another  symptom  of 
degeneration.  Dying  cells  in  abundance  may  be  observed  in  epithelia, 
where  formerly  they  were  often  regarded  as  peculiar  kinds  of  cells  (cf. 
also  Fig.  1 6). 

The  groivth  of  cells  preeminently  concerns  the  protoplasm  and  only 
exceptionally  takes  place  equally  in  all  directions,  in  which  case  the 
original  form  of  the  cell  is  retained  (e.g.,  egg-cell);  as  a  rule,  an  un- 
equal growth  occurs.  As  a  result  of  unequal  growth  the  original 
form  is  altered  ;  the  cell  becomes  elongated,  or  flattened,  or  branched, 
etc.  The  majority  of  cells  are  soft  and  susceptible  to  change  in  form 
from  mechanical  influences,  as,  for  example,  the  columnar  epithelial-cells 
in  the  empty  bladder,  which  are  flattened  in  the  distended  organ.  Epithe- 
lial-cells of  the  peritoneum  may  through  stretching  acquire  three  times 
their  original  superficies. 

Secretory  Products  of  Cells. — The  secreted  materials  are  either  wholly 
removed  (as  most  glandular  secretions)  or  they  harden  and  remain  on 
the  surface  of  the  cells.  To  the  latter  belong  certain  intercellular  sub- 
stances, many  of  which  are  a  secretion  of  cells  ;  others  are  produced  by 
a  transformation  of  the  peripheral  layers  of  the  cell-protoplasm,  still 
others,  by  a  complete  metamorphosis  of  the  cells  themselves  (?).  It  is 
very  difficult  to  decide  whether  individual  intercellular  substances  were 
formed  by  one  process  or  another  ;  many  points  in  this  matter  are  still 
the  subject  of  lively  controversy. 


64 


HISTOLOGY. 


The  intercellular  substances  occur  either  in  small  amount,  as  struc- 
tureless, soft,  perhaps  fluid,  cement-substance,  between  epithelial-cells, 
connective-tissue  cells,  smooth  muscle-fibers,  etc.  ;  or  in  large  amounts, 
exceeding  the  mass  of  the  cells,  and  are  then  called  matrix  or  ground- 
substance.  The  matrix  is  either  formless  (homogeneous)  or  formed  ;  in 
the  latter  case  it  is  for  the  most  part  transformed  into  fibers  or  granules 
of  different  kinds.  The  remnants  of  formless  substance  found  between 
the  fibers  or  granules  are  also  called  cement-substance. 


TECHNIC. 

No.  i. — For  the  study  of  nuclear  structure  and  karyokinesis  am- 
phibian larvae  are  most  suitable.  Those  most  readily  procured  are  the 
larvae  of  the  water-salamander,  which  in  the  months  of  June  and  July 
abound  in  every  pool.  Place  freshly-caught  specimens,  3  to  4  cm.  long, 
in  about  100  c.c.  of  chromic-acetic  acid  (p.  22).  After  three  hours  place 
the  larvae  in  running  water  for  eight  hours,  and  then  in  70  per  cent,  alco- 
hol. At  the  expiration  of  four  hours,  or  later,  the  objects  are  ready  for 
further  treatment. 

a.  Nuclear  Structure. — With  a  scalpel  carefully  scrape  the  epithe- 
lium from  the  skin  of  the  abdomen,  with  two  pairs  of  fine  forceps  strip 
off  the  thin  corium,  stain  it  from  one  to  three  minutes  in  5  c.c.  of  Hansen's 
hematoxylin  (p.  36),  and  mount  in  damar-varnish  (p.  45).  Between  the 
round  glands  beautiful  connective-tissue  cells  with  large  nuclei  may  be 

seen.  The  reticulum  of  the  proto- 
plasm, the  centrosome  and  attraction- 
sphere,  and  the  finer  structure  of  the 
nucleus  can  only  be  recognized  by  the 
employment  of  complicated  methods 
and  high  magnification.  The  results 
obtained  by  ordinary  methods  are 
like  that  pictured  in  Fig.  6. 

The  cross-striped  muscles  of  the 
tail  and  the  membranes  of  smooth 
muscle-fibers  (the  latter  may  be  readily 
obtained  by  stripping  off  the  muscu- 
laris  of  the  intestine)  also  furnish  in- 
structive slides. 

b.  Karyokinesis. — With  a  pair  of 
fine  scissors  cut  round  the  margin 

of  the  cornea,  and  strip  off  the  same  ;  stain  and  preserve  as  in  a.  The 
preparation  must  be  placed  on  the  slide  with  the  convex  surface  of  the 
cornea  upward  ;  in  the  epithelium,  even  with  the  low-power  objective, 
many  karyomitotic  figures  may  be  seen,  which  are  recognized  by  their 
intense  color.  By  this  method  the  nuclear-spindle  and  polar-radiation, 
as  in  Fig.  5,  can  only  be  perceived  (with  higher  magnification)  in  espe- 
cially favorable  preparations,  e.  g.,  eggs  of  siredon  and  of  the  trout. 


Protoplasm. 


Nucleus 


1  Nuclear  membrane. 

2  Chromatin-cords. 

3  Nucleoli. 


FIG.  6  —CONNECTIVE-TISSUE  CELL  FROM 
CORIUM  OF  TRITON  T^ENIATUS.  SURFACE 
VIEW.  X  560.  Only  the  coarser  filaments 
of  the  nuclear  network  can  be  distinctly 
seen ;  with  this  magnification  the  finer  fila- 
ments appear  as  minute  dots,  the  nucleoli  as 
parts  of  the  nuclear  network. 


TISSUES.  65 

The  delicate  lamellae  suspended  from  the  convex  side  of  the  carti- 
laginous gill-arch,  as  well  as  the  epithelium  of  the  floor  of  the  oral  cavity, 
are  suitable  objects.  Occasionally  not  a  single  karyokinetic  figure  is 
found.  Isolated  figures  may  sometimes  be  observed  in  preparation  a. 


B.    TISSUES. 

i.   THE  EPITHELIAL  TISSUES. 

The  elements  of  epithelial  tissue,  the  epithelial-cells,  are  sharply 
defined  cells  consisting  of  protoplasm  and  nucleus.  A  cell-membrane 
is  frequently  absent,  often  is  represented  by  a  condensation  of  the  periph- 
eral zone  of  the  protoplasm.  The  majority  of  epithelial-cells  are  soft 
and  plastic,  yield  readily  to  the  pressure  of  neighboring  cells,  the  result 
of  which  is  great  diversity  of  outline.  In  general  two  principal  forms 
can  be  distinguished:  \h<t  flattened  or  squamous  and  the  cylindrical  or 
columnar  (better,  prismatic).  These  extremes  are  united  by  numerous 
transitional  forms. 

The  squamous  epithelial-cells  are  rarely  symmetrical  in  form,  except- 
ing the  pigmented  epithelium  of  the  retina,  which  consists  of  tolerably 
regular  hexagonal  cells  ;  generally  the  contour  is  very  irregular. 


FIG.  7. — ISOLATED  EPITHELIAL  CELLS  OF  RABBIT.  X  560.  i.  Squamous  cells  (mucous  membrane  of 
mouth).  Techn.  No.  90.  2.  Columnar  cells  (corneal  epithelium).  3.  Columnar  cells,  with  top-plate,  J 
(intestinal  epithelium).  4.  Ciliated  cells:  h,  cilia  (bronchial  epithelium).  Techn.  on  p.  28. 

The  cylindrical  epithelial-cells,  cylinder  or  columnar  cells,  seen  from 
the  side  are  elongated  elements,  the  height  of  which  considerably  exceeds 
the  breadth  ;  seen  from  above  they  appear  hexagonal ;  they  are  therefore 
in  reality  prismatic. 

Cells  as  high  as  they  are  broad  are  called  cubical  epithelial-cells  ; 
sometimes,  pavement-cells  ;  but  since  any  form  of  epithelium  viewed 
from  the  free  surface  may  present  a  mosaic,  the  term  pavement  is  not 
distinctive. 

Many  columnar  cells  have   a   sometimes  homogeneous,  sometimes 
striated   border  on   their    free   upper    surface  (Fig.   7,  3  s),    a  cuticular 
formation,  the  so-called  top-plate. 
S 


66  HISTOLOGY. 

The  striae  are  the  optical  expression  of  minute  rods,  occasionally 
distinctly  seen  even  with  medium  magnification  (Fig.  9  c)  ;  they  are 
processes  of  the  protoplasm  that  penetrate  the  homogeneous  cuticular 
zone,  and  differ  greatly  in  length.  To  the  same  category  belong  the  stria- 
tions  seen  in  the  basal  half  of  the  cells  lining  the  smaller  ducts  of  the 
salivary  glands  and  in  the  cells  of  some  of  the  tubules  of  the  kidneys  ; 
in  the  latter  they  form  the  so-called  "  brushbofder,"  and  are  distinguished 
by  their  greater  delicacy. 

Other  columnar  cells  are  b^set  with  delicate  filamentous  processes 
(cilia)  on  their  free  surface,  that  during  life  are  in  constant  active  vibra- 
tion to  and  fro  in  a  definite  direction.  These  are  called  ciliated  cells. 

The  specially-differentiated  neuro-epithelial  cells  will  be  described 
in  connection  with  the  organs  of  special -sense. 

..:••&*.>  ^ 


FlG.   8.— PlGMENTED  EPITHELIUM  OF  THE  RETINA 

OF  MAN.  Viewed  from  the  surface.  X  560.  Techn. 
No.  173.    _ 


* 

FIG.  9.— SIMPLE  COLUMNAR  EPITHELIUM  OF  SMALL 

INTESTINE  OF  MAN.   X  560.    c.  Striated  cuticular  FIG.     10.— STRATIFIED     SQUAMOUS     EPITHELIUM 

border,    z.  Columnar  cell.    tp.  Tunica  propria.  (LARYNX  OF  MAN).  X  240.  i.  Columnar  cells.  2. 

Techn.  like  No.  102.  Prickle-cells.  3.  Squamous  cells.  Techn.  No.  122. 

Continuous  layers  of  epithelial-cells,  covering  outer  and  inner  sur- 
faces of  the  body,  are  called ."  epithelia."  The  epithelia  are  sometimes 
composed  of  a  single  stratum,  sometimes  of  several  strata,  and,  accord- 
ingly, the  following  varieties  are  distinguished  : 

I.  Simple  squamous  epithelium:  in  the  outer  layer  of  the  retina,  the 
alveoli  of  the  lungs,  the  rete  vasculosum  Halleri,  the  membranous  laby- 
rinth, the  choroid  plexuses  and  parts  of  the  ventricles  of  the  brain,  the 
posterior  surface  of  the  anterior  capsule  of  the  lens,  in  parts  of  the  ducts 
of  glands,  in  the  Malpighian  corpuscle  and  descending  limb  of  Henle's 
loop  in  the  kidney  ;  also  in  the  peritoneum,  the  articular  cavities,  the 
tendon-sheaths,  the  bursae,  the  blood-  and  lymph-vessels.  The  five  last- 
mentioned  epithelia  are  also  called  endothelia — their  elements,  endothe- 
lial-cells. 


TISSUES.  67 

2.  Simple  columnar  epithelium :  in   the   intestinal  canal   and   in  the 
ducts  of  many  glands. 

3.  Simple  ciliated  epithelium  :  in  the  smallest  bronchi,  in  the  uterus 
and  oviducts,  in  the  accessory  spaces  of  the   nasal  fossae,  in   the   central 
canal  of  the  spinal  cord. 

4.  Stratified  squamons  epithelium  ;  not  all  the  elements  of  which  are 
flattened  cells  :  the  lowermost  stratum  is  composed  of  columnar  cells  ; 
superposed   on   this  are  several  strata  of  variously-shaped  cells,  mainly 
irregular  polygonal  prickle-cells,  over  which  lie  successive  strata  of  cells 
that  as  they  approach  the  surface  become  progressively  thinner  and  flat- 
ter (Fig.  10).     The  stratified  squamous  epithelium  occurs  in  the  mouth 
and  pharynx,  in  the  esophagus,  on  the  vocal  cords,  on  the  cornea,  in  the 
vagina,  and   in  the  female   urethra.     The  epidermis   also   consists  of  a 
stratified  pavement  epithelium,  but  is  characterized  by  the  cornification 
of  the  cells  of  the  superficial  strata,  which  are  transformed  into   horny 
scales  without  nuclei.      Cornified  cells  are  also  found  on   the  hairs  and 
nails,  but  in  these  situations  they  are  nucleated. 

5.  Stratified  columnar  epitJielinm  :  in   man   is   found   only  on    the 
conjunctiva  palpebrarum,  in  the  main  excretory  ducts  of  certain  glands, 
and  in  a  portion  of  the  male  urethra.      The  arrangement  of  the  strata  is 
similar  to  that  of — 

6.  Stratified  ciliated  epithelium :  only  the  most  superficial  cells  are 
columnar  and  bear  cilia  ;  in  the  deepest  layers  the  elements   are   mainly 
spherical  ;  in   the  middle  layers,  spindle-shaped 

(Fig.  11).  Stratified  ciliated  epithelium  is  found 
in  the  larynx,  in  the  trachea,  in  the  larger 
bronchi,  in  the  nasal  fossae,  in  the  upper  part 
of  the  pharynx,  in  the  Eustachian  tube,  and  in 
the  epididymis. 

Between  the  epithelial-cells  extremely  nar- 
row clefts  often  occur, — intercellular  spaces,— 
which  are  occupied  by  a  soft,  perhaps  fluid,  inter- 

FIG.    ii.  — STRATIF!BD     CILI- 

ccllular  substance.  *      In  many  epithelia — perhaps        ATED   EPITHELIUM,    x  560. 

From   the    respiratory   nasal 

all  the  columnar  epithelia  of  the  mucous  mem-        mucous  membrane  of  man. 

i.    Oval    cells.       2.    Spindle- 

branes— and  in  the  majority  of  the  glandular  epi-        SS^T^to.  N30.  S!ur 

thclia,  the  intercellular  spaces  are  closed  toward 

the  free  surface  by  very  delicate  bars  of  a  peculiar  cement-substance  ; 

*  Since,  in  the  human  skin,  the  intercellular  spaces  have  been  successfully  injected 
through  the  lymph- vessels,  it  was  believed  that  this  substance  is  identical  with  ordinary  lymph. 
This,  however,  is  not  correct,  for  the  intercellular  substance  of  epithelium  reacts  differently;  it 
becomes  black  when  treated  with  silver  nitrate. 


68 


HISTOLOGY. 


since  these  bars — "  terminal  bars"  (Schlnssleisteii) — are  connected  with 
one  another  they  form  a  "  network  of  terminal  bars"  (Schlussleistennetz\ 
in  the  meshes  of  which  the  ends  of  the  epithelial-cells  directed  toward 
the  free  surface  are  inserted. 


Top-plate. 


Cross-sections'    \ 
of    the    ter-       1 
minal  bars.  \ 

B- 


Network  of  ter- 
minal bars. 


Top-plate. 


Intercellular 
substance. 


FIG.  12. — COLUMNAR  EPITHELIUM  OF  AN  INTES- 
TINAL VILLUS  OF  MAN.  Magnified  about  600 
times.  Network  of  terminal  bars:  A,  view  of 
free  surface  ;  B,  lateral  aspect ;  on  the  left  the 
cross-sections,  on  the  right  the  lateral  surfaces  of 
the  terminal  bars  are  seen. 


FIG.  13.— SCHEME  OF  THE  NETWORK  OF  TER- 
MINAL BARS.  The  two  cells  on  the  left  are 
divided  lengthwise  into  halves ;  the  two  on 
the  right  are  drawn  as  complete  cylinders  or 
prisms. 


The  union  of  the   epithelial-cells  is  effected  in  such  a  manner  that 
either  they  present  smooth  surfaces  of  contact  to  one  another,  namely 

by   the   intervention  of   intercellular   substance, 
or  they  interlock  by  variously-shaped  processes, 
^"0:          *  the  latter  being  pressure-effects.      The  delicate 

:^,::^     ^>  ,  spines   and    thorns  visible    on    the    surfaces    of 

many  epithelial-cells  have  been  regarded  as 
similar  processes.  But  these  are  connecting- 
filaments,*  which  pierce  the  intercellular  sub- 
stance and  establish  an  intimate  union  with 
neighboring  epithelial-cells.  Cells  provided 
with  such  spikes  and  ridges  are  called  prickle- 
cells  ;  the  processes  are  aptly  designated  by  the  appropriate  name  of 
intercellular-bridges  (Fig.  14). 

They  were  first  seen  on  the  polygonal  cells  of  stratified  squamous 


FIG.  14. — FROM  A  VERTICAL 
SECTION  OF  THE  STRATUM 
GERMINATIVUM  OF  THE  EPI- 
DERMIS. X  560.  Seven 
prickle-cells  united  by  inter- 
cellular bridges.  Techn.  like 
No.  83. 


*  These  filaments,  that  can  be  traced  in  the  interior  of  the  cells  (the  spongioplasm, 
p.  56),  are  the  ground  on  which  such  epithelium  was  said  to  have  a  "  fibrillar  "  structure, — a 
designation  that  can  only  lead  to  perplexity,  because,  for  example,  it  tends  to  produce  con- 
fusion with  the  fibrillar  structure  of  connective  tissue,  which  is  something  wholly  different. 


TISSUES.  69 

epithelium,*  but  they  also  occur  on  the  cells  of  simple  squamous  and 
columnar  epithelium,  for  example,  of  the  stomach  and  of  the  intestines,  but 
there  they  are  extremely  delicate  and  can  be  demonstrated  only  by  the 
application  of  special  methods.  The  length  of  the  intercellular-bridges 
and  the  diameter  of  the  "  intercellular  clefts  "  occurring  between 
them  vary  greatly  in  the  different  forms  of  epithelium  and  in  the  different 
physiologic  states  of  the  tissue. 

The  epithelium  has  no  blood-  and  lymph-vessels,  but  nerves  are 
found  in  some  situations,  for  example,  in  the  epithelium  of  the  skin  and 
of  many  mucous  membranes. 

Secretory  Activity  of  Epithelial  Tissue. — Many  epithelial-cells 
are  capable  of  secreting  and  discharging  certain  substances  which  are 
not  used  in  the  growth  and  development  of  the  tissue.  Such  cells  are 
called  glandular  cells.  The  secreted  substances  are  either  used  in  the  body 
(secretions)  or,  those  of  no  further  use,  removed  from  the  body  (excre- 


cf  be 

FIG.  15. — SECRETING  EPITHELIAL-CELLS.  From  a  thin  section  of  mucous  membrane  of  the  stomach  of 
man.  X  560.  p.  Protoplasm,  s.  Secretion,  a.  Two  cells  empty  of  secretion  ;  the  cell  between 
them  shows  beginning  mucoid  metamorphosis,  e.  The  cell  on  the  right  is  discharging  its  contents, 
its  upper  free  wall  having  ruptured  ;  the  granular  protoplasm  has  increased,  and  the  nucleus  has 
become  round  again.  Techn.  No.  102. 

tions).  The  performance  of  the  processes  of  elaboration  and  discharge 
of  secretions  (or  excretions)  is  manifested  by  certain  changes  in  the 
appearance  of  the  form  and  contents  of  glandular  cells,  which  indicate 
states  of  rest  and  activity.  In  many,  e.  g.,  serous  glandular  cells,  the 
differences  (barring  certain  phenomena  in  the  nucleus)  are  confined  to 
decrease  in  volume  and  a  dark  appearance  of  cells  empty  of  secretion, 
and  to  increase  in  volume  and  a  clear  appearance  of  those  filled  with 
secretion.  In  other  gland-cells,  e.  g.,  in  many  mucous  glands,  the 
process  of  secretion  can  be  more  closely  traced.  Granular  protoplasmic 
contents  and  a  usually  oval,  nearly  centrally-situated  nucleus  indicate  a 
condition  of  exhaustion.  The  elaboration  of  secretion  begins  at  the  free 
surface  of  the  cell,  that  directed  toward  the  lumen  of  the  gland,  and 
manifests  itself  by  the  transformation  of  the  granular  protoplasm  into  a 
clear  mass  (b,  s\  more  or  less  sharply  defined  against  the  still  unaltered 

*The  basal  surface  of  the  columnar  cells  of  stratified  squamous  epithelium  are  also  pro- 
vided with  short  processes,  directed  toward  the  subjacent  connective  tissue,  the  "rivet-fibers" 
(ffaftfasern},  that  are  rendered  visible  only  by  means  of  complicated  methods. 


7O  HISTOLOGY. 

protoplasm  (b,  p).  As  the  process  of  secretion  progresses,  more  and 
more  of  the  protoplasm  is  transformed,  and  the  nucleus  and  remnant  of 
unaltered  protoplasm  are  pushed  to  the  bottom  of  the  cell ;  as  a  conse- 
quence of  this  compression  the  nucleus  gradually  becomes  rounded  or 
even  flattened.  The  volume  of  the  cell  when  filled  with  secretion  is 
considerably  increased.  Finally,  the  cell-wall  bursts  at  its  free  surface. 
The  secretion  gradually  escapes,  simultaneously  the  protoplasm  is  regen- 


Secretion. 
Protoplasm  with  nucleus. 


Gland  lumen.  — 


if  If 

fi>  — f     L-,  <Jv' 


FIG.  16. — CRYPT  OF  LIEBERKUHN  FROM  A  SECTION  OF  THE  LARGE  INTESTINE  OF  MAN.  X  165.  The 
secretion  formed  in  the  goblet-cells  is  dark  in  color.  In  zone  i  the  goblet-cells  show  the  beginning  of 
secretion.  That  a  part  of  the  secretion  is  already  given  off  here  is  evident  from  the  presence  of 
secretion  in  the  form  of  drops  in  the  lumen  of  the  crypt.  2.  Goblet-cells  with  much  secretion. 
3.  Cells  containing  a  small  amount  of  secretion.  4.  Degenerating  goblet-cells,  some  of  which  still 
contain  remnants  of  secretion.  Techn.  on  p.  29. 

crated,  the  nucleus  moves  upward  to  its  original  position,  and  the  cell, 
diminished  in  size,  is  restored  to  its  previous  condition  and  appearance. 
The  majority  of  glandular  cells  do  not  degenerate  in  the  act  of  secretion, 
but  are  able  to  repeat  the  process  aga"in  and  again.  The  sebaceous  glands 
furnish  an  exception,  for  their  secretion  is  formed  by  the  disintegration 


TISSUES.  7 1 

of  cells,  like  the  goblet-cells.*  In  the  case  of  the  latter  the  processes  of 
elaboration  and  of  expulsion  of  secretion  occur  simultaneously  (Fig.  1 6)  ; 
at  first  the  secretion  is  produced  more  rapidly  than  it  is  discharged  and 
it  accumulates  in  the  cell  (Fig.  16,  2),  but  finally  expulsion  exceeds 
production,  the  cell  gradually  empties  itself  completely,  and  dies 
(Fig.  1 6,  4). 

The  glandular  cells  lie  isolated  between  other  epithelial-cells  f  or 
are  united  in  groups  and  form  glandular  tissue. 

Supplement.  The  Glands.  The  glands  are  composed  almost  ex- 
clusively of  epithelium.  Connective  tissue  and  blood-vessels,  so  impor- 
tant from  a  physiologic  point  of  view,  are  morphologically  subordinate. 
Therefore,  although  they  are  organs,  they  may  be  appropriately  described 
with  the  epithelial  tissues. 

The  glands  are  secreting  epithelial  tissue,  buried  beneath  the  sur- 
face of  the  body,  which  is  arranged  in  the  form  of  cylindrical  tubules  or 
rounded  saccules.  Accordingly,  two  principal  forms  of  glands  are 
distinguished  :  tubular  and  saccular  (alveolar)  glands. 

The  tubular  glands  occur  singly  or  united  in  groups  ;  therefore  they 
are  divided  as  follows  : 

1.  Simple    tubular  glands,   which    have    the    form    of    simple    or 
branched    tubules    (Fig.     17);     the    latter    may    be    called    a    "tubular 
system." 

2.  Compound   tubular  glands,    which    consist  of   a  large,  variable 
number  of  "tubular  systems"  (Fig.  17). 

The  same  division  is  applicable  to  alveolar  glands.  They  also  may 
be  distinguished  as — 

1.  Simple  saccular  (alveolar}  glands,  which,  similarly,  are  simple  or 
branched  saccules  having  an  excretory  duct ;  the   latter  form  is  termed 
an  "alveolar  system." 

2.  Compound  saccular  (alveolar]  glands,  which  consist  of  a  com- 
bination of  several  "alveolar  systems"  (Fig.  17). 

Simple  unbranched  tubular  glands  :  the  peptic  or  fundus  glands,  the  sweat- 
glands,  and  the  glands  of  Lieberkiihn. 

Simple  branched  tubular  glands  :  the  pyloric  glands,  the  glands  of  Brunner, 
the  smallest  glands  of  the  oral  cavity,  the  glands  of  the  tongue,  and  the  glands  of 
the  uterus. 

Compound  tubular  glands  :  the  mammary,  the  salivary,  the  lacrymal,  and  the 


*The  testicle  and  ovary  afford  a  peculiar  instance,  the  gland-cells  of  which  after  secre- 
tion undergo  further  development. 

f  They  are  then  called  unicellular  glands  ;  they  are  very  common  among  invertebrates, 
also  occur  in  man  as  goblet-cells. 


/2  HISTOLOGY. 

larger  mucous  glands,*  the  kidneys,  the  glands  of  Covvper,  the  prostate  gland,  the 

Tubular  Glands. 


Simple  tubule. 


Terminal  compartments. 
Simple  Glands.  Compound  Glands. 

Saccular  (Alveolar)  Glands. 

_^^  ___^___^__^— _ A 

Simple  saccule. 


Terminal  Saccules  (Alveoli). 

compartments. 


Simple  Glands.  Compound  Glands. 

FIG.  17. — DIAGRAM  OF  THE  DIFFERENT  GLAND-FORMS,    a.  Excretory  duct. 


*The  cross-sections  of  the  coiled  and  closely-packed  branching  tubules  of  the  last  four 
glands  were  for  a  long  time  regarded  as  vesicular  evaginations  of  the  terminal  ends  of  the 
tubules,  and  were  named  acini.  Such  evaginations  (except  in  a  few  isolated  parts  of  the  sub- 


TISSUES.  73 

thyroid  gland,  the  testicle,  and  the  liver.  The  branches  in  the  last  two  anastomose 
and  form  networks,  hence  they  are  also  called  "  reticular  glands." 

Simple  unbranched  saccular  glands:  the  smallest  sebaceous  glands  and  the 
follicles  of  the  ovary. 

Simple  branched  saccular  glands  :  the  larger  sebaceous  glands  and  the  Meibo- 
mian  glands. 

Compound  saccular  glands:  the  lungs. 

In  the  majority  of  glands,  particularly  in  those  visible  to  the  naked 
eye,  a  sheath  is  formed  by  the  surrounding  connective  tissue,  which 
sends  septa  into  the  gland  and  divides  it  into  compartments  of  varying 
size,  the  gland  lobules.  The  septa  are  the  carriers  of  the  larger 
blood-vessels  and  nerves.  The  glands  may  secrete  throughout  their 
entire  extent,  but  usually  only  that  part  lying snear  the  blind  end,  the 
fumlus,  is  specialized  for  this  purpose,  while  the  part  forming  the  con- 
nection with  the  surface  serves  for  the  conveyance  of  the  secretion,  and 
is  called  excretory  duct. 

Glands  without  excretory  ducts  are  the  thyroid  body  and  the  ovary. 
The  former  has  an  excretory  duct  in  the  embryonic  period,  which  dis- 
appears in  the  course  of  development.  The  gland  follicles  of  the  ovary, 
in  an  embryonal  period,  also  are  in  connection  with  the  superficial  epi- 
thelium ;  these  connections,  which  might  be  called  excretory  ducts, 
disappear  and  the  expulsion  of  the  products  formed  in  the  ovary  (the 
ova)  takes  place  by  the  bursting  of  the  follicles.  The  ovary  is  a 
dehiscent  gland. 

The  secreting  portion  of  all  glands  consists  of  a  usually  simple 
layer  of  gland-cells,  which  bound  the  lumen  of  the  gland  and  are  in  turn 
surrounded  by  a  special  modification  of  the  connective  tissue,  the  mcm- 
brana  propria  or  basement  membrane*  (see  p.  Si).  On  the  outer  side  of 
the  basement-membrane  the  blood-vessels  are  situated  (Fig.  1 8).  Hence 
the  gland-cells  are  inserted  between  the  blood-vessels  and  the  lumen  of 
the  gland,  and  on  the  peripheral  side  receive  from  the  blood-vessels  (or 
from  the  neighboring  lymph-vessels)  the  materials  necessary  for  secre- 


lingual  gland)  do  not  really  occur ;  the  diameter  of  the  lumen  is  not  greater  here  than  in  other 
portions  of  the  tubules.  On  the  other  hand,  a  thickening  of  the  wall  of  terminal  parts  of 
tubules,  by  taller  cells,  is  not  uncommon  in  some  tubular  glands,  e.g.,  in  the  parotid  and  the 
pancreas.  Such  thickenings,  however,  must  not  be  called  "acini,"  since  we  understand  by 
acinus,  an  evagination,  a  distention  of  the  lumen.  To  avoid  misunderstanding,  the  term 
"  acinus  "  was  dropped  and  that  of  "  alveolus  "  selected  for  glands  of  the  saccular  form.  The 
much-used  term  "  acinous  "  or  "  racemose  "  has  also  been  discarded,  because  the  cross-sections 
of  tubular  glands  also  exhibit  a  "racemose  "  appearance. 

*  Occasionally,  instead  of  this,  the  gland-tubules  are  embraced  by  stellate,  nucleated  cells 
("basket-cells"). 


74 


HISTOLOGY. 


tion,  on  the  other  or  central  side  yield  the   elaborated    substances   as 
secretion. 

In  many  glands,  for  example,  the  mucous  and  the  serous  glands  of 
the  oval  cavity,  the  glands  of  the  stomach,  of  the  duodenum,  and  of 
the  pancreas,  the  secretion  is  discharged  not  only  on  the  side  of  the  cell 
directed  toward  the  lumen,  but  on  many  sides.  Then  the  secretion 
passes  into  minute  canaliculi,  which,  simple  or  branched,  sometimes 
without  anastomoses,  sometimes  forming  a  network,  surround  the  gland- 
cell.*  These  minute  canaliculi,  the  "secretory  capillaries,"  open  indi- 
vidually or  united  in  a  single  larger  trunk  into  the  lumen  of  the  gland  ; 
whether  they  are  always  present  or  only  periodically  is  not  yet  deter- 
mined. 


Gland-lumen. 


Gland-cells. 


Membrana  pro- 
pria  (basement 
membrane). 


-.-    Blood-vessels. 


Lumen. 


Secretory 
capillaries. 


"W. 


FIG.  18. — SECTION  OF  A  Mucous  GLAND  OF 
THE  TONGUE  OF  RABBIT.  Blood-vessels  in- 
jected. The  nuclei  of  the  gland-cells  were  only 
faintly  visible  in  the  preparation.  X  180.  Techn. 
like  No.  n8b. 


FIG.  19.— SECTION  OF  FUNDUS  GLAND  OF  MOUSE. 
Left  upper  half  drawn  after  an  alcohol  prepara- 
tion (Techn.  No.  102),  right  upper  half  after  a 
Golgi  preparation  (Techn.  No.  119).  The  entire 
lower  portion  is  a  diagrammatic  combination  of 
both  preparations. 


The  microscopic  appearance  of  the  gland-cells  changes  with  the 
periodic  functional  condition.  In  some  glands  all  the  cells  simultane- 
ously exhibit  the  same  functional  appearance.  In  other  glands  different 
functional  states  are  encountered  at  the  same  time,  even  within' the  same 
tubule  or  alveolus.  The  latter  is  the  case  in  many  mucous  glands,  the 
cells  of  which  have  delicate  walls.  Tubules  occur  in  these  that  con- 
tain cells  in  a  condition  of  activity  and  of  exhaustion.  The  loaded  cells 
push  the  empty  ones  away  from  the  gland-lumen  ;  the  latter  then  lie  at 
the  periphery  of  the  tubule  and  represent  in  this  form  the  so-called 
"demilunes  of  Heidenhain  "  or  "crescents  of  Gianuzzi "  (Fig.  20). 
The  nuclei  of  many  glandular  cells  also  exhibit  varying  appearances 
corresponding  to  the  changing  functional  condition  ;  in  empty  cells  the 


It  may  be  that  single  parts  of  the  canaliculi  lie  in  the  interior  of  the  gland-cell. 


TISSUES. 


75 


nucleus  exhibits  a  delicate  chromatin-network  and  a  conspicuous  nucle- 
olus  (Fig.  20,  I  //),  while  in  loaded  cells  the  nucleolus  is  invisible  and  the 
chromatin-cords  appear  in  the  form  of  coarse  fragments  (Fig.  20,  I  a). 

The  smaller  branches  of  the  ducts  of  many  tubular  glands  must  be 
regarded  as  belonging  to  the  secreting  portion,  since  they  are  charac- 
terized by  the  specialized  epithelium  lining  their  walls  and  participate  in 
the  function  of  secretion  by  eliminating  certain  materials  (salts).  They 
are  not  only  excretory  ducts,  but  part  of  the  actively-secreting  portion 
of  the  gland.  The  difference  in  the  structure  of  these  branches  renders 
their  division  into  two  parts  desirable  :  the  first  portion,  proceeding  from 
the  terminal  compartments,  is  narrow  and  lined,  sometimes  with  flat, 


FIG.  20.— DIAGRAM  OF  THE  ORIGIN  OF  THE  CRESCENTS.     Protoplasm  shown  deeply  shaded,  the  secre- 
tion less  shaded. 


I.  Cross-section  of  a 
tubule  of  a  mucous 
gland,  with  six  gland- 
cells.  Three  («i,  Oo,a3) 
are  filled  with  secretion, 
and  have  pressed  the 
three  cells  (£,,  t>2,  £3) 
empty  of  secretion 
away  from  the  gland- 
lumen.  Comp.  Fig. 
166. 


II.  Same  section 
somewhat  later.  The 
cells  #1,  an,  03  have 
discharged  a  part  of 
their  secretion  and  be- 
come smaller.  The 
cells  £],  &>•  ^3  again 
extend  to  the  lumen 
and  begin  to  secrete. 


III.  Same  section 
still  later.  The  cells 
a\,  <*•>>  03  have  dis- 
charged the  bulk  of 
their  secretion  and  be- 
come still  smaller.  In 
the  cells  b\,  &>i  £3  the 
secretion  has  accumu- 
lated to  such  an  extent 
that  they  are  the  larger 
and  compress  their 
neighbors,  a\,  a»,  03. 


In  I  the  cells  £,  in  IV  the  cells  a,  are  the  crescents. 


IV.  Same  section  still 
later.  The  cells  a\,  o», 
03  ate  now  entirely 
empty  and  pressed 
away  from  the  gland- 
lumen  by  di,  b-2,  £3,  now 
full  of  secretion. 


sometimes  with  cubical,  cells  ;  it  is  called  the  intercalated  or  intermediate 
tubule.  The  adjoining  portion  is  wider  and  clothed  with  tall  columnar 
cells,  the  bases  of  which  show  distinct  longitudinal  striation  ;  it  is  called 
the  intralobular  or  secretory  (salivary  or  mucous)  tube.  The  relative 
length  of  the  intercalated  tubules  and  the  intralobular  tubes  varies 
greatly  in  the  different  glands. 

The  excretory  ducts  consist  of  a  simple  or  stratified  columnar  epi- 
thelium lining  a  wall  of  connective  tissue  mingled  with  elastic  fibers. 

The  most  complex  glands  consist  of  the  following  sections  :  (i) 
The  excretory  duct,  which  divides  into  (2)  the  secretory  tubes,  which 
lead  into  (3)  the  intercalated  tubules,  which  pass  into  (4)  the  terminal 
compartments,  which,  finally,  take  up  (5)  the  secretory  capillaries. 


76 


HISTOLOGY. 


TECHNIC. 

No.  2. — To  obtain  living  ciliated-cells,  kill  a  frog  (p.  27),  place  it  on 
its  back,  and  with  scissors  cut  off  the  lower  jaw,  so  that  the  roof  of  the 
cavity  of  the  mouth  is  exposed.  From  the  mucosa  of  the  roof  cut  out 
a  small  strip  about  5  mm.  long,  place  it  on  the  slide  in  a  drop  of  salt 
solution,  and  apply  a  cover-glass.  Examine  with  the  high  power  and 
search  the  edges  of  the  preparation.  At  first  the  movement  of  the  cilia 
is  very  lively,  so  that  the  observer  cannot  see  the  individual  cilia ;  the 
entire  ciliated  border  waves  ;  the  motion  has  been  compared  to  that  of  a 
corn-field  swayed  by  the  wind.  After  a  few  moments  the  rapidity  of  the 
movement  diminishes  and  the  cilia  can  be  plainly  seen.  If  the  move- 
ment ceases,  it  can  be  restored  by  the  application  of  a  drop  of  concen- 
trated potash  solution  (p.  22)  ;  the  effect  is  transient,  so  that  the  eye  of 
the  observer  must  not  be  removed  from  the  ocular  while  the  fluid  passes 
under  the  cover-glass.  The  addition  of  water  soon  suspends  the  move- 
ment. 


FIG.  21. — FROM  A  CROSS-SECTION  OF  THE  UMBILI- 
CAL CORD  OF  A  FOUR  MONTHS'  HUMAN  EMBRYO. 
X  240.  i.  Cells.  2.  Intercellular  substance.  3. 
Connective-tissue  bundles  mostly  in  oblique  sec- 
tion, at  4  in  true  cross-section.  Techn.  No.  3. 


FIG.  22.— CONNECTIVE-TISSUE  BUNDLES  OF  VARI- 
OUS THICKNESSES  FROM  THE  INTKRMUSCULAR 
CONNECTIVE  TISSUE  OF  MAN.  X  240.  Techn. 
No.  4. 


II.  THE  SUPPORTING  TISSUES. 

While  in  the  epithelial  tissues  the  cells  constitute  the  principal  mass, 
in  the  supporting  tissues  the  intercellular  substance  (ground-substance, 
matrix)  is  conspicuously  developed  and  variously  differentiated.  The 
predominance  of  the  intercellular  substance,  which  also  functionally 
plays  the  more  important  part,  is  characteristic  of  the  group  of  support- 
ing tissues.  According  to  the  nature  of  the  intercellular  substance  they 
are  divided  into  :  (i)  connective  tissue  ;  (2)  cartilage  ;  (3)  bone. 

i.  Connective  Tissue. — The  matrix  or  intercellular  substance  of 
connective  tissue  is  more  or  less  soft  ;  the  cells  are  few  in  number. 


TISSUES. 


77 


Several   varieties  are   distinguished  :  (a)    mucous   connective  tissue,  (ft) 
fibrillar  connective  tissue,  and  (c)  reticular  connective  tissue. 

(a)  Mucous  connective  tissue  consists  of  round  or  stellate  branched 
cells   and   a  large  quantity  of  undifferentiated,  muciferous    intercjjplar 
substance  containing  a  few  minute  bundles  of  fine  fibrils.      In  the  higher 
animals  it  is  found  only  in  the  umbilical  cord  of  very  young  embryos, 
but  it  is  widely  distributed  in  many  lower  animals. 

(b)  Fibrillar  connective  tissue  consists  of  abundant  intercellular  sub- 
stance and  of  cells. 

The  intercellular  substance  is  composed  of  fibrils,  that,  according  to 
one  view,  are  a  metamorphosis  of  the  matrix  ;  according  to  another,   a 


FIG.  23.— ELASTIC  FIBERS.  X  560.  A.  Fine  elastic  fibers:  /,  from  intermuscular  connective  tissue  of 
man  ;  b,  connective-tissue  bundles  swelled  by  treatment  with  acetic  acid.  Techn.  No.  n.  B.  Very 
thick  elastic  fibers  :  /,  from  ligamentum  nuchse  of  ox  ;  b,  connective-tissue  bundles.  Techn.  No.  12. 
C.  From  a  cross-section  of  the  ligamentum  nuchae  of  ox ;/,  elastic  fibers;  b,  connective-tissue  bun- 
dles. Techn.  No.  13. 


direct  transformation -pro  duct  of  the  cell-substance.  They  are  exquis- 
itely fine  filaments  (0.6  /*),  which  are  united  by  a  small  quantity  of 
homogeneous  cement-substance  into  bundles  varying  in  thickness,  the 
connective-tissue  bundles.  These  bundles  are  soft,  flexible,  slightly 
extensible,  and  characterized  by  their  pale  contour,  their  longitudinal 
striation,  their  wavy  course,  and  by  their  chemical  properties.  On 
treatment  with  picric  acid  they  separate  into  their  fibrils,  swell  on  the 
addition  of  dilute  acids,  e.  g.%  acetic  acid,  and  become  transparent,  are 
destroyed  by  alkaline  fluids,  and  on  boiling  yield  glutin. 

The  matrix  of  fibrillar  connective  tissue  always  contains  elastic  fibers, 
but  in  different  quantities  (Fig.  23).  In  contrast  to  the  connective-tissue 
bundles  they  are  characterized  by  their  sharp,  dark  outlines,  their  strong 


7  5  HISTOLOGY. 

refractive  power,  and  their  conspicuous  resistance  to  acids  and  alkalies. 
The  elastic  fibers  vary  from  immeasurably  fine  to  1 1  //,  and  usually 
occur  in  the  form  of  finer  or  coarser  networks,  the  meshes  of  which  are 
sometimes  narrow,  sometimes  large. 

Narrow-meshed  networks  composed  of  thick  elastic  fibers  form  the 
transition  to  elastic  membranes,  which  are  either  homogeneous  or  finely 
striated  and  perforated  with  apertures  of  different  sizes  (hence  the  name 
fenestrated  membranes),  and  probably  are  produced  by  the  merging  of 
broad  elastic  fibers  (Fig.  24). 

When  the  quantity  of  elastic  fibers  predominates  over  the  number 
of  connective-tissue  bundles,  the  tissue  is  spoken  of  as  elastic  tissue. 


FIG.  24.— Network  («)  of  thick  elastic  fibers, 
on  the  left  passing  into  a  fenestrated  mem- 
brane, m.  From  the  endocardium  of 
man.  X  560.  Techn.  No.  14. 


FIG.  25.— A.  Connective-tissue  cells  from  intermuscular 
connective  tissue.  X  560.  i.  Flat  cell  lying  partly  on  a 
connective-tissue  bundle;  2,  folded  cell  ;  3,  cell  of  which 
the  protoplasm  is  not  visible;  d,  connective-tissue  bun- 
dles. Techn.  No.  5.  B.  Connective-tissue  bundles  with 
encircling  fibers  ;  /&,  nucleus.  Techn.  No.  8.  C.  Plasma- 
cells  from  the  eyelid  of  a  child.  Techn.  No.  184. 


The  elastic  fibers  are  derived  neither  from  cells  nor  from  nuclei,'  but 
are  transformations  of  the  matrix,  perhaps  of  the  existing  connective- 
tissue  bundles.  In  the  beginning  of  their  development  they  are  thin, 
but  become  thicker  with  advancing  growth. 

The  connective-tissue  cells  are  irregularly  polygonal  or  stellate, 
much  flattened,  variously  bent  or  folded  (Fig.  25,  A).  The  flattening 
and  bending  are  explained  by  the  adaptation  of  the  cells  to  the  narrow 
spaces  occurring  between  the  connective-tissue  bundles.  Not  infre- 
quently the  flattened  cells  form  complete  sheaths  about  the  connective- 
tissue  bundles.  If  such  a  bundle  be  treated  with  acetic  acid,  it  swells 
and  bursts  the  ensheathing  cells,  of  which  annular  or  other-shaped 
fragments  remain  and  constrict  the  swelled  bundle.  Formerly  these 


TISSUES. 


79 


remnants   of  cells   were   considered   fibers,  and  were  called    "  encircling 

o 

fibers  "  (Fig.  25,  B).     Other  connective-tissue  cells  are  spherical,  rich  in 
protoplasm,    coarsely   granular,   and    relatively   of  large  size  ;  they  are 
termed  plasma-cells  and  are  found  principally 
in   the   neighborhood  of  small   blood-vessels  3 

(Fig.  25,  C).  Others  again,  the  mast- 
cells,  are  characterized  by  the  affinity  of 
their  protoplasm  for  certain  anilin  dyes  (e.  g., 
dahlia),  but  do  not,  as  their  name  may  suggest, 
stand  in  any  demonstrable  relation  to  the  pro- 
cesses of  nutrition.  (They  are  also  known 
as  granule-cells^)  The  protoplasmic  body 
of  the  connective-tissue  cells  encloses  a 
nucleus  and  often  contains  pigment-granules  ; 
in  the  latter  case  they  become  pigment-cells, 

that  in  man  are  found  only  in  certain  parts  of  the  skin  and  of  the  eye, 
but  in  the  lower  animals  are  very  common.  Connective-tissue  cells 
may  contain  fat-globules,  that,  when  they  are  very  large,  coalesce 
and  give  a  spherical  form  to  the  cell,  which  is  then  designated  a  fat- 
cell  (Fig.  26).  .  In  such  cells  the  protoplasm  occupies  only  a  nar- 


FIG.  26.— FAT-CELLS  FROM  THE 
AXILLA  OF  MAN.  X  240.  i.  'Ihe 
equator  of  the  cell  in  focus  ;  2, 
objective  somewhat  elevated  ;  3, 
4,  forms  changed  by  pressure;  p, 
traces  of  protoplasm  in  the  vicin- 
ity of  the  flat  nucleus,  k.  Techn. 
No.  9. 


Surface-view  of  fat-cells,  in  the  nuclei  of  which  vacuoles  are  visible. 


Blood-vessel  with  blood-corpuscles. 


A  fat-cell  and  its  nucleus 
in  profile. 


Blood-capillary.  Fibrillar  connective  tissue. 

FIG.  27.— ADIPOSE  TISSUE  FROM  THE  HUMAN  SCALP.    X  240  (about).    Techn.  No.  10. 


row  peripheral  zone,  in  which  lies  the  extremely  flattened  nucleus, 
that  in  well-developed,  but  not  in  atrophic,  fat-cells  invariably  con- 
tains one  or  more  sharply-circumscribed  vacuoles.  These  finally 


8o 


HISTOLOGY. 


pass  into  the  interior  of  the  fat-cell,  whereupon  new  vacuoles  form 
within  the  nucleus.  The  protoplasmic  zone  is  often  so  thin  as  to 
be  invisible.  Aggregations  of  fat-cells  are  abundantly  supplied  with 
blood-vessels,  lymph-vessels,  and  nerves,  and  form  what  is  called  adipose 
tissue,  which  bears  a  very  important  physiologic  relation  to  metabolism. 
In  cases  of  extreme  emaciation  the  fat  in  fat-cells  is  reduced  to  a  few 
small  globules.  In  place  of  the  fat  which  has  disappeared  there  is  a 
pale  protoplasm  mixed  with  a  mucoid  fluid ;  the  cell  is  no  longer 
spherical,  but  has  become  flattened.  Such  cells  are  named  serous  fat- 
cells  (Fig.  28).  In  many  fat-cells  after  death  spherical  masses  of  needle- 
shaped  crystals  appear,  the  so-called  margarin  crystals. 

Finally,  smaller  irregularly-spherical  cells   are  found  in  connective 
tissue  that  are  not   connective-tissue  elements,  but  leucocytes  that  have 

passed  out  of  the  blood-vessels. 
They  are  described  as  wandering 
cells,  in  distinction  to  those  of  the 
connective  tissue,  which  are  desig- 
nated as  fixed  cells  ;  a  classification 
that  cannot  be  rigidly  carried  out, 
since  in  some  conditions  (mainly 
pathologic)  the  fixed  connective- 
tissue  cells,  also  epithelial  and 
glandular  cells,  can  migrate,  and 
it  is  therefore  better  to  term  the 
latter  "  histogenetic,"  the  leuco- 
cytes "  hematogenetic  "  wandering 
cells.  It  is  self-evident  that  such 
in  the  same  category  with  the 


FIG.  28. — SEROUS  FAT-CELLS  FROM  THE  AXILLA 
OF  AN  EXTREMELY  EMACIATED  INDIVIDUAL.  X 
240.  k.  Nucleus  ;  f,  oil-droplets,  c,  Blood-capilla- 
ries; £,  connective-tissue  bundles.  Techn.  No.  9. 


wandering  cells   cannot  be  included 
leucocytes. 

The  number  and  distribution  of  the  different  kinds  of  cells  are 
subject  to  considerable  fluctuation. 

The  different  elements  of  fibrous  connective  tissue  are  united  either 
without  exact  arrangement,  as  in  areolar  tissue,  or  are  regularly  disposed 
in  definite  structures.  Areolar  tissue  is  distinguished  by  its  loosely- 
connected  bundles  of  fibers  interlacing  in  every  direction  ;  it  occurs 
between  neighboring  organs  and  serves  to  connect  them  and  to  fill  in 
the  interspaces.  For  this  reason  it  is  also  called  "interstitial"  tissue. 
The  cells  of  areolar  tissue  not  infrequently  contain  fat.  The  fibrous 
connective  tissue  characterized  by  closer  connection  and  regular  arrange- 
ment of  the  bundles  comprises  the  corium,  the  serous  membranes,  the 
periosteum,  the  perichondrium,  the  tendons,  the  fasciae,  the  ligaments  ; 


TISSUES. 


8l 


the  compact  sheaths  of  the  central  nervous  system,  of  the  blood-vessels, 
of  the  eye,  and  of  many  glands. 

The  fibrous  connective  tissue  in  immediate  contact  with  epithelium  is 
usually  modified,  forming  a  structureless  membrane  called  basement 
membrane  or  membrana  propria,  also  Jiyaloid  membrane.  The  membrana 
propria  of  many  glands,  for  example,  the  salivary  glands,  consists  of 
flattened,  often  stellate  cells,  which,  basket-like,  surround  the  gland- 
tubules. 

(r)  Reticnlar  Connective  Tissue. — The  views  in  regard  to  the  structure 
of  reticular  connective  tissue  are  divided.  According  to  an  opinion 


Connective-tissue 
cells. 


Network,   sr^ 


Leucocytes. 


FIG.  30.— RETICULAR  CONNECTIVE  TISSUE.    From  a 
FIG.  29.-A  PIF.CE  OF  THE  GREATER  OMENTUM  OF  ?,!ial5en  section  of  a  human   lymph-gland.     X   560. 


MAN.     :\  60.     Techn.  No.  15. 


Techn.  No.  50. 


formerly  widely  entertained,  it  consists  of  a  delicate  network  of  anasto- 
mosing stellate  cells.  To  this  may  be  traced  the  name  "  cytogenous," 
that  is,  formed  of  cells,  and  accordingly  mucous  tissue  may  be  termed 
cytogenous  tissue.  There  is  no  doubt  that  such  networks  occur  in  lower 
animals  and  in  embryonic  stages  of  higher  animals.  But  in  the  higher 
vertebrates  the  relations  are  changed  ;  here  the  network  consists  of  slender 
bundles  of  fibrillar  connective  tissue,  upon  which  lie  flattened,  nucleated 
cells  (Fig.  30).  By  means  of  complicated  methods  the  outlines  of  the  cells 
on  the  fibers  can  be  demonstrated.  In  fibrillar  connective  tissue  the 
6 


82  HISTOLOGY. 

cells  almost  without  exception  lie  upon  the  fibers.  Finally,  the  fact  that 
even  in  the  adult  fibrillar  connective  tissue  may  change  into  reticular 
tissue  can  be  comprehended  only  on  the  assumption  that  the  latter  is  a 
network  of  delicate  fiber-bundles.  Therefore  reticular  connective  tissue 
really  is  only  a  variety  of  fibrillar  connective  tissue.  The  meshes  of 
reticular  connective  tissue  are  usually  crowded  with  leucocytes.  It 
principally  occurs  in  lymph-glands  and  is  then  called  adenoid  tissue. 

2.  Cartilage. — The  matrix  of  cartilage  is  firm,  elastic,  easily  cut,  and 
milk-white  or  yellowish  in  color.  The  cells  present  little  that  is  charac- 
teristic in  form  ;  usually  they  are  spherical  or,  from  being  flattened  on 
one  side,  somewhat  angular.  They  lie  in  the  spaces  or  lacuna  of  the 


ft  A 


:  \ 

y— ;  •—          -  ^ 


V. 


FIG.  31.—  HYALINE  CARTILAGE.  X  240.  A.  Surface  view  of  the  ensiform  process  of  frog,  fresh  ;  p,  proto- 
plasm of  cartilage-cell,  which  entirely  fills  the  lacuna;  £,  nucleus  ;  g,  hyaline  matrix.  Techn.  No.  16. 
B.  Portion  of  cross-section  of  human  rib-cartilage  several  days  after  death,  examined  in  water:  the 
protoplasm,^,  of  the  cartilage-cells  has  withdrawn  from  the  walls  of  the  lacunae,  h;  the  nuclei  are 
invisible,  i.  Two  cells  within  one  capsule,  £/  x,  a  developing  partition.  2.  Five  cartilage-cells 
within  one  capsule  ;  the  lowest  cell  has  fallen  out,  so  that  only  the  empty  cavity  is  seen.  3.  Capsule 
cut  obliquely,  and  apparently  thicker  on  one  side.  4.  Capsule  not  cut,  but  showing  the  cell  within. 
g.  Hyaline  matrix  transformed  into  rigid  fibers,/".  Techn.  No.  17. 

matrix,  which  they  completely  fill.  Whether,  as  in  bone,  the  matrix  is 
penetrated  by  a  system  of  minute  channels  communicating  with  and  con- 
necting the  lacunae  is  extremely  doubtful.  Many  observations  in  which 
such  channels  apparently  were  perceived  have  been  acknowledged  as 
erroneous  ;  the  supposed  channels  were  a  result  of  shrinkage,  and  can  be 
produced  by  treating  cartilage  with  absolute  alcohol  or  ether.  Not  infre- 
quently the  matrix  immediately  surrounding  the  lacunae  is  specialized, 
and  forms  a  strongly  refractive,  occasionally  concentrically-striated  cap- 
sule. The  matrix  is  produced  by  the  cartilage-cells  ;  it  originates  in 
secretions  that  subsequently  fuse  into  a  homogeneous  mass.  The  parts 
lying  nearest  to  the  cells,  immediately  adjoining  the  capsule,  are  the 


TISSUES. 


'83 


youngest ;  they  do  not  always  persist,  but  during  the  process  of  cell- 
division  are  resorbed.  Thus  the  ground-substance  is  subjected  to  many 
changes.  It  may  be  free  from  fibrous  admixture  or  it  may  be  penetrated 
by  elastic  fibers  or  by  connective-tissue  bundles.  Accordingly  three 
varieties  are  distinguished  :  (a)  hyaline  cartilage,  (li)  clastic  cartilage,  (c) 
fibro-cartilage . 

(a)  Hyaline  cartilage  is  of  a  faint  bluish,  pearly  color.  It  occurs  as 
the  cartilages  of  the  respiratory  organs  and  of  the  nose,  as  the  costal  and 
the  articular  cartilages,  also  in  the  synchondroses,  and  in  the  embryo  in 
many  situations  where  it  is  later  replaced  by  bone.  It  is  characterized 
by  the  homogeneity  of  its  matrix,  which  in  the  ordinary  methods  of 
investigation  appears  amorphous  throughout,  but  after  special  processes, 
e.  g.,  artificial  digestion,  falls  apart  into  bundles  of  fibers.  Further 
evidence  in  confirmation  of  its  fibrillar  structure  is  afforded  by  its  appear- 


FIG.  32. — ELASTIC  CARTILAGE.  X  240.  i.  Portion  of  section  of  the  vocal  process  (anterior  angle)  of  aryte- 
noid  cartilage  of  a  woman  thirty  years  old  ;  the  elastic  substance  in  the  form  of  granules.  2  and  3. 
Portions  of  sections  of  the  epiglottis  of  a  woman  sixty  years  old  ;  a  fine  network  of  elastic  fibers  in  2,  a 
coarser  network  in  3.  z.  Cartilage-cell,  nucleus  not  visible  ;  £,  capsule.  Techn.  No.  18. 

ance  when  examined  in  polarized  light.  It  is  very  firm,  very  flexible,  and 
on  boiling  yields  cJwndrin. 

In  certain  cases  the  matrix  may  undergo  peculiar  modifications.  In 
the  thyroid  and  costal  cartilages  it  is  transformed  patchwise  into  rigid 
fibers,  that  impart  an  asbestos-like  luster,  perceptible  on  macroscopic  in- 
spection. In  advanced  age  deposition  of  calcareous  salts  may  take  place 
in  the  hyaline  matrix,  in  the  beginning  appearing  in  the  form  of  minute 
granules,  subsequently  as  complete  husks  surrounding  and  enclosing  the 
cells.  In  the  cartilages  of  the  larynx  this  may  occur  as  early  as  the 
twentieth  year. 

The  cells  of  hyaline  cartilage  frequently  occur  in  groups  or  nests, 
an  arrangement  explained  by  the  conditions  and  processes  of  growth. 
Two  cells  may  lie  in  one  lacuna  and  be  enclosed  within  the  same  capsule 
(Fig-  31,  B  i);  they  are  the  descendants  of  one  cell  which  has  under- 


84  HISTOLOGY. 

» 

gone  division  by  the  indirect  mode  ;  in  some  cases,  a  thin  partition  of 
hyaline  substance  may  be  seen  between  two. such  cells.  In  other  cases 
the  septum  does  not  develop  immediately,  and  the  process  of  cell-division 
may  be  repeated  until  groups  of  four,  eight,  and  even  more  cells  may  be 
enclosed  within  one  capsule  (Fig.  31,  £>,  2).  Such  phenomena  were  sup- 
posed to  establish  a  special  theory  of  cell-division,  the  so-called  en- 
dogenous cell-formation.  Not  infrequently  the  cartilage-cells  in  adults 
contain  oil-globules. 

(fr)  Elastic  cartilage  has  a  faint  yellowish  color.      It  occurs  as  the 
cartilages  of  the  external  ear,  of  the  epiglottis,  of  Wrisberg  and  Santorini, 
and  of  the  vocal  process  (anterior  angle)  of  the  arytenoid  cartilages.      It 
presents  the  same  structural  peculiarities  as  hyaline  cartilage,  but  is  dis- 
tinguished by  the  networks  of  finer  or 
coarser  elastic  fibers  that  penetrate  the 
matrix.      The  elastic  fibers  do  not  arise 
directly  from   the   cartilage-cells,  but 
by  a  transformation  of  the  matrix,  and 
appear  in  the  vicinity  of  the  former  as 
minute  granules,    that    later   are    dis- 
1  posed   in   linear   rows    and   fuse    into 

®/'  fibers.     This  phenomenon,   according 

to  an  opposite  view,  is  regarded  as  an 

i     . ,,  indication  of  post-mortem  disintegra- 

tion of  the  elastic  fibers. 

FIG.  33.-FROM  A  HORIZONTAL  SECTION  OF  /   \    Fihro.cartUao-c  is  found  in  the 

THE     INTERVERTEBRAL     DlSC    OF      MAN.     g.  \C  )     r iU '  U    «*'***«£* 

Fibrillar  connective  tissue;  z,  cartilage-cell        •     ,          ~,-f~Kt-n1     ^t'c^c      fli^     ™iKiV      cwm 
(nucleus   invisible);   k,   capsule  surrounded        mterVCl  tebral     CllSCS,    tllC     pUblC      Sym- 
by   calcareous  granules.       X   240.       Techn.  ,         •        ,1  r  MI  J   j-t 

NO.  19.  physis,  the  inferior  maxillary  and  the 

sterno-clavicular   articulations.       The 

matrix  contains  an  abundance  of  fibrous  connective  tissue  in  loose 
bundles  extending  in  every  direction  (Fig.  33,£~).  The  cartilage-cells 
are  few  in  number,  have  thick  capsules,  and  occur  in  small  groups  or 
rows  at  comparatively  wide  intervals. 

3.  Bone.— The  matrix  of  bone,  osseous  tissue,  is  distinguished  by 
its  hardness,  solidity,  and  elasticity,  properties  due  to  an  intimate  blend- 
ing of  organic  and  inorganic  substances.  This  union  is  of  such  a  nature 
that  either  part  may  be  removed  without  destroying  the  structure  of 
the  tissue.  On  treatment  with  acids.,  the  inorganic  substances  are 
withdrawn  ;  the  bone  is  decalcified,  is  rendered  flexible,  and  is  easily  cut, 
like  cartilage.  The  organic  substances  may  be  removed  by  cautious 
heating ;  the  bone  is  then  said  to  be  calcined.  Similarly,  fossil  bones 
are  deprived  of  the  organic  substances  through  the  prolonged  action 


TISSUES.  O  5 

v 

of  moisture.  The  matrix  or  ground-substance  is  composed  of  calcium 
salts,  chiefly  basic  calcium  phosphate,  and  of  collagenous  fibrils,  that  are 
united  by  a  small  amount  of  cement-substance  in  finer  or  coarser  bundles  ; 
accordingly,  a  fine-textured,  or  lamellar,  and  a  coarse-textured,  or  plexiform 
matrix  are  distinguished.  It  appears  homogeneous  or  faintly  striated  and 
contains  numerous  spindle-shaped  spaces  I  5  to  27  //  in  length,  the  lacuiue, 
which  communicate  with  one  another  through  numerous  branched  minute 
canals,  the  canaliculi.  In  this  way  a  system  of  canaliculi  that  penetrates 
the  entire  matrix  is  established.  Within  the  lacunae,  sometimes  improperly 
called  "bone-cells,"  lie  nucleated,  flattened,  oval  bodies,  the  real  bone- 
cells.  It  is  doubtful  whether  in  the  adult  the  bone-cells  are  connected  by 
means  of  processes  extending  through  the  canaliculi,  although  such  con- 
nection is  readily  observed  in  developing  bone.* 


Fie.  34. — FROM  A  GROUND  SECTION  OF  DRIED 
BONE  OF  ADULT  MAN;  /t,  lacunae;  k,  canalic- 
uli ;  g,  bone-matrix.  A.  Seen  from  the  surface. 
B.  Seen  from  the  side.  X  560.  Techn.  No.  56. 


FIG.  35.— FROM  SECTIONS,  a,  OF  THE  HUMERUS 
OF  A  FOUR  MONTHS'  HUMAN  EMBRYO;  d,  of 
the  middle  turbinal  bone  of  adult  man  ;  z,  bone- 
cells  lying  in  the  lacunae,  h  ;  the  canaliculi  are  only 
partially  visible  ;  g,  matrix.  X  560.  Techn. No.  62. 


Fibrous  connective  tissue  and  cartilage  may  be  converted  directly 
into  osseous  tissue  by  calcification  of  the  matrix  ;  the  connective-tissue 
cells  or  cartilage- cells  then  become  bone-cells.  However,  this  process 
is  of  comparatively  rare  occurrence.  Usually  the  formation  of  osseous 
tissue  takes  place  in  such  a  way  that  the  ground-substance  of  the  con- 
nective tissue  or  of  the  cartilage  calcifies  during  embryonic  life.  Around 
the  trabeculae  of  the  calcified  matrix  numerous  young,  still  indifferent, 
connective-tissue  cells  then  arrange  themselves,  which  produce  the  at 
first  soft,  then  calcified,  ground-substance  of  bone.  These  cells  are 


*  The  skeleton  of  the  adult  is  principally  formed  of  the  fine-textured  matrix,  which  is 
characterized  by  the  arrangement  of  the  fiber-bundles  in  lamellae  and  contains  elastic  fibers. 
The  coarse-textured  matrix  occurs  in  the  fetus  in  periosteal  and  intermembranous  bone,  and  is 
found  in  the  adult  along  sutures  and  at  the  point  of  insertion  of  tendons  ;  it  always  contains 
uncalcified  connective-tissue  bundles,  the  so-called  Sharpey's  fibers,  which  also  are  found  in 
the  circumferential  and  interstitial  lamellre  of  fine-textured  bone,  the  remains  of  the  primary 
or  periosteal  bone. 


86  HISTOLOGY. 

called  osteoblasts.  At  first  they  lie  upon  the  osseous  matrix  they  have 
formed,  later  they  come  to  lie  within  it,  and  gradually  become  trans- 
formed into  stellate  bone-cells. 

Dentine  is  a  modification  of  bone,  from  which  it  is  distinguished  by 
its  developmental  history  ;  the  formative  cells,  the  odontoblasts,  are  not 
enclosed  within  the  matrix,  but  penetrate  the  latter  with  their  processes. 
Further  details  will  be  found  in  Connection  with  the  structure  of  teeth. 

Blood-vessels,  Lymphatics,  and  Nerves. — The  supporting  tissues  are, 
in  general,  poorly  supplied  with  blood-vessels,  lymph-vessels,  and  nerves. 
An  exception  occurs  in  adipose  tissue,  which  has  a  rich  vascular  supply. 
But  connective  tissue  plays  a  very  important  part  as  a  conveying  appa- 


Bone-matrix. 


Osteoblasts.   — =-^r"~ — '~$~ 


Bone-cell. — 

I 


m 


Osteoblast  changing 
to  a  bone-cell. 


FIG.  36.—  PORTION  OF  CROSS-SECTION  OF  THE  DIAPHYSIS  OF  THE   HUMERUS  OF  A  FOUR   MONTHS' 
HUMAN  EMBRYO.     X  560.    Techn.  No.  62. 

ratus  in  the  transference  of  nutritive  fluids  —  tissue  -juices,  lympli  —  from  the 
blood-vessels  to  the  tissues.  When  the  matrix  is  soft,  as  in  mucous 
tissue,  the  lymph  permeates  the  entire  substance  ;  when  on  the  other 
hand  it  is  denser,  the  lymph  circulates  in  a  system  of  intercommunicating 
channels,  a  juice-canal-system,  formed  by  the  cell-spaces  —  lymph-spaces  — 
and  the  minute  canals  connecting  them  —  lymph-capillaries.  This  is  the 
case  in  bone  and  the  more  compact  connective  tissues.  Whether  the 
tissue-juice  is  diffused  throughout  the  matrix  of  hyaline  cartilage  or 
conveyed  in  definite  channels  is  still  undetermined.  The  intercellular 
substance  of  epithelium  is  in  direct  connection  with  the  lymph-capillaries 
of  the  subjacent  connective  tissue,  and  may  be  regarded  as  being  similarly 
permeated  by  the  lymph. 


TISSUES. 


TECHNIC. 

No.  3. — Mucous  Connective  Tissue. — Place  the  umbilical  cord  of  a 
three  or  four  months'  human  embryo  (or  pig  embryo  from  three  to  six  cm. 
long)  in  100  c.c.  of  Miiller's  fluid  (p.  21)  for  three  or  four  weeks  ;  harden 
in  30  c.c.  of  gradually  strengthened  alcohols  (p.  33).  The  cord  will  still 
be  very  soft ;  in  order  to  obtain  good  sections  it  must  be  embedded  in 
liver,  and  in  cutting  must  be  somewhat  compressed  with  the  fingers. 
The  section  may  be  stained  in  picrocarmine  (twelve  hours)  or  in  hema- 
toxylin  (five  minutes),  and  should  be  examined  in  a  drop  of  distilled 
water.  In  glycerol  and  in  damar-varnish  the  delicate  processes  of  the 
cells  and  the  bundles  of  connective  tissue  are  invisible.  In  the  vicinity 
of  the  blood-vessels  the  network  of  cells  is  less  fine  ;  therefore  a  field 
remote  from  the  blood-vessels  should  be  selected  for  study.  The  older 
the  embryo,  the  greater  is  the  number  of  the  connective-tissue  bundles. 
Mount  in  diluted  glycerol  (p.  22). 

No.  4.  —  Fibrous  Connective  Tissue ;  Connective-tissue  Bundles.— 
Prepare  small  strips,  one  or  two  cm.  long,  of  intermuscular  connective 
tissue,  for  example,  of  the  thin  septum  between  the  serratus  and  inter- 
costal muscles  ;  place  a  small  piece  on  a  dry  slide  and  quickly  spread  it 
out  with  teasing  needles  (see  "half-drying  method"  No.  29  a,  p.  1 06), 
add  a  drop  of  salt  solution  and  apply  a  cover-glass.  The  bundles  of 
connective  tissue  appear  wavy  and  pale  ;  with  a  little  practice  the  sharply- 
contoured,  highly- refracting  elastic  fibers  may  be  distinguished  and  also, 
in  favorable  situations,  the  nuclei  of  the  connective-tissue  cells. 

No.  5. — The  cells  of  fibrous  connective  tissue  may  be  rendered  visible 
by  the  addition  of  a  drop  of  picrocarmine  to  preparation  No.  4,  under  the 
cover-glass  (p.  48).  In  most  cases  only  the  red  nucleus  can  be  per- 
ceived, especially  when  the  cell  lies  wholly  upon  the  fibrous  bundles. 
In  rare  cases  the  pale  yellow,  variously-shaped  body  of  the  cell  can  be 
seen  (Fig.  25,  A,  i,  2,  3). 

No.  6. — Mast-cells  (granule-cells). — Fix  small  pieces,  i  or  2  cm. 
square,  of  mucous  membrane  (of  the  mouth,  pharynx,  or  intestine)  in 
ninety-five  per  cent,  alcohol  (p.  30).  In  from  three  to  eight  days  cut 
thin  sections  and  stain  them  in  10  c.c.  of  alum-carmine  dahlia  for 
twenty-four  hours  (p.  25).  Transfer  them  to  10  c.c.  of  absolute  alcohol 
for  twenty-four  hours,  which  must  be  renewed  once  or  twice  during  this 
time.  Mount  in  damar  (p.  45).  The  protoplasm  of  the  mast-cells 
exhibits  granules  stained  an  intense  blue. 

No.  7. — Fibrillce. — Place  a  piece  of  tendon  about  2  cm.  long  in  a 
saturated  aqueous  solution  of  picric  acid.  On  the  following  day,  with 
two  pairs  of  forceps,  pull  the  tendon  apart  along  its  length,  take  from  the 
interior  a  bundle  about  5  mm.  long,  and  tease  the  same  on  a  dry  slide 
(cf.  No.  29  a,  p.  1 06) ;  add  a  drop  of  distilled  water,  apply  a  cover-glass, 


HISTOLOGY. 


and  examine  with  the  high -power  objective, 
as  exceedingly  fine,  silky  filaments. 


The  ultimate  fibrillae  appear 


Xo.  8. — "Encircling  Fibers!' — With  the  scissors  cut  out  a  piece 
about  one  cm.  square  of  the  connective  tissue  within  the  arterial  circle  of 
Willis,  wrash  it  in  a  watch-glass  in  salt  solution,  with  needles  spread  it 
out  in  a  drop  of  the  same  solution  on  a  slide,  and  cover.  With  the  low 
power,  in  addition  to  numerous  delicate  blood-vessels  and  ordinary 
bundles  of  fibrous  tissue,  sharply-contoured,  refracting  bundles,  in 
distinct  contrast  to  the  remaining  connective  tissue,  will  be  found,  which, 
on  the  use  of  the  high  power  and  a  diaphragm  of  narrow  aperture,  show 
that  they,  likewise,  consist  of  fibrillar  connective  tissue.  Place  such  a 
bundle  in  the  field  and  treat  it  with  a  drop  of  acetic  acid,  under  the 
cover-glass  (p.  48).  So  soon  as  the  acid  reaches  the  bundle,  it  swells, 
the  fibrillation  vanishes,  and  instead  elongated  nuclei  appear.  The 
swelling  is  not  uniform  ;  at  irregular  intervals  the  bundle  is  constricted. 
With  dim  illumination  the  "  fibers  "  (cell-remnants)  producing  the  con- 
strictions may  be  seen  (Fig.  25,  B\ 


Fat-cells  in  a 
sjmple  layer  ; 


in  superposed 
layers. 


Fibrillar  con- 
nective tissue. 


FIG.  37. — ADIPOSE  TISSUE  FROM  A  SECTION  OF  HUMAN  SCALP.    X  50.    Techn.  No.  161. 


No.  9. — Fat-cells. — Take  a  small  piece  of  the  reddish-yellow,  gela- 
tinous fat  from  the  axilla  of  an  emaciated  individual  ;  rapidly  spread  out 
a  piece  the  size  of  a  split  pea  in  the  thinnest  possible  layer  on  a  dry  slide, 
immediately  add  a  drop  of  salt  solution  and  apply  a  cover-glass.  In 
thin  places  atrophic  fat-cells,  like  those  shown  in  Fig.  28,  will  be  seen. 
This  preparation  may  be  stained  under  the  cover-glass  with  picrocarmine 
(p.  48)  and  preserved  in  diluted  glycerol.  Ordinary  (normal)  fat-cells, 
taken  from  any  part  of  the  body,  are  likewise  to  be  examined  in  salt 
solution.  The  spherical  cells  should  be  studied  with  change  of  focus 
(tf.  Fig.  26). 

No.  10. — Adipose  tissue  may  be  seen  in  sections  of  many  prepara- 
tions fixed  by  any  of  the  usual  methods — above  all  of  the  skin  (cf.  Fig. 
238  and  243).  The  oily  contents  are  withdrawn  by  the  treatment  with 


TISSUES.  89 

alcohol  and  then  the  clusters  of  empty  cell-envelopes  present  a  picture 
that  the  beginner  often  finds  difficulty  in  understanding. 

No.  n. — pine  elastic  fibers  may  be  readily  obtained  by  treating 
preparation  No.  4,  under  the  cover-glass,  with  a  few  drops  of  acetic  acid. 
The  connective-tissue  bundles  swell  and  become  transparent ;  the  elastic, 
fibers,  on  the  contrary,  remain  unaltered,  and  stand  out  sharply  con- 
toured (Fig.  23,  A). 

No.  1 2. — Thicker  elastic  fibers  may  be  obtained  by  teasing  in  a  drop 
of  salt  solution  a  slender  piece,  about  5  mm.  long,  of  the  fresh  ligamen- 
tum  nuchae  of  an  ox  (Fig.  23,  R).  The  piece  should  not  be  taken  from 
the  loose,  enveloping  tissue,  but  from  the  tough,  yellowish,  fibrous  por- 
tion. The  preparation  may  be  stained  in  picrocarmine  and  mounted  in 
glycerol. 

No.  13. — Cross-sections  of  thick  clastic  fibers  maybe  obtained  by 
drying  a  piece  (10  cm.  long  and  from  I  to  2  cm.  thick)  of  the  ligamentum 
nuchae  (it  will  be  ready  to  use  in  four  or  six  days)  and  treating  it  like 
No.  64. 

No.  14. — Fenestrated  Membranes. — Take  a  small  piece  (about  5  mm. 
square)  of  endocardium,  place  it  in  a  drop  of  water  on  a  slide,  and  add, 
under  the  cover-glass,  I  or  2  drops  of  potash-lye.  Examine  the  edges 
of  the  preparation  (Fig.  24). 

Good  specimens  may  also  be  obtained  from  the  basilar  artery  ;  place  a 
piece  of  the  artery  cut  open  lengthwise  in  10  c.c.  of  concentrated  potash 
solution.  After  six  hours  take  a  small  piece,  about  I  cm.  long,  and 
separate  the  lamellae  in  a  drop  of  water  on  a  slide  ;  this  is  easily  done 
by  scraping  with  a  scalpel.  Cover  and  examine  with  the  high  power. 
The  small  apertures  in  the  membrane  have  the  appearance  of  shining 
nuclei. 

With  the  low  power  the  membrane  is  recognized  by  its  dark  outlines. 
To  preserve,  wash  it  well  in  10  c.c.  of  water  (five  minutes),  stain  it  in 
3  c.c.  of  congo-red  for  from  twelve  to  twenty  hours  (p.  25),  and  mount 
in  damar. 

No.  15. — A  i^vork  of  connective-tissue  bundles  may  be  obtained 
by  spreading  out  a  little  piece  of  fresh  human  omentum  in  a  few  drops 
of  picrocarmine.  It  may  be  preserved  in  diluted,  non-acidulated  glycerol 
(p.  22).  Pieces  of  the  omentum  fixed  in  absolute  alcohol  and  stained 
with  hematoxylin  and  eosin  (p.  37)  may  be  mounted  in  damar- varnish 
(p.  45).  (Fig.  29,  p.  8  i.) 

No.  1 6. — Hyaline  Cartilage. — Cut  off  the  extremely  thin  episternum 
of  the  frog,  place  it  on  a  dry  slide,  cover  it  with  a  cover-glass,  and 
examine  at  once  with  the  high  power.  The  cartilage-cells  completely 
fill  the  lacunae  (Fig.  31,  A).  For  prolonged  study,  add  a  drop  of  saline 
solution. 

No.  1 7. — Hyaline  Costal  Cartilage. — Without  any  previous  prepara- 
tion thin  sections  of  costal  cartilage  may  be  cut  with  a  dry  razor  and 
examined  in  a  drop  of  water.  Search  for  one  of  the  glossy  areas  con- 


9O  HISTOLOGY. 

taining  rigid  fibers  (Fig.  31  B).     The  preparation  may  be  preserved  by 
adding  a  few  drops  of  dilute  glycerol. 

Fresh  cartilage  does  not  readily  stain.  The  tissue  must  be  first 
placed  in  Kleinenberg's  picrosulphuric-acid  mixture  or  in  Miiller's  fluid, 
then  in  alcohol  (p  33),  and  subsequently  stained  with  Hansen's  hema- 
toxylin  (p.  36).  Mounted  in  damar,  which  clears  vigorously,  the  finer 
details  vanish. 

No.  1 8, — Elastic  Cartilage. — Take  a  piece  of  the  arytenoid  cartilage 
of  man  (better  still  of  the  ox) — the  elastic  cartilage  of  the  anterior  angle 
is  recognized  by  its  yellowish  color.  Cut  a  section  that  includes  the 
boundary  line  between  the  elastic  and  hyaline  cartilage,  and  examine  it  in 
water.  Preserve  like  No.  17.  The  development  of  the  elastic  fibers  may 
often  be  studied  in  the  cartilages  of  adults,  especially  in  the  epiglottis  and 
in  the  vocal  process  of  the' arytenoid  cartilage  (Fig.  32,  i). 

No.  19. —  White  Fibro- cartilage. — Cut  the  intervertebral  discs  of 
adult  man  in  pieces  from  I  to  2  cm.  square  ;  fix  in  100  c.c.  of  picrosul- 
phuric  acid  (p.  21)  for  twenty-four  hours  and  harden  in  50  c.c.  of  gradually 
strengthened  alcohols  (p.  33).  Stain  sections  in  Hansen's  hematoxylin 
(p.  36)  and  mount  in  damar  (p.  45).'  Sections  through  the  edges  yield 
hyaline  cartilage  ;  through  the  central  portions  of  the  disc  they  exhibit 
large  groups  of  cartilage-cells. 


III.    THE  MUSCULAR  TISSUES. 

The  structural  elements  of  the  muscular  tissues,  the  muscle-fibers  ^ 
occur  in  two  forms,  the  smooth  and  the  striated.  Both  are  cells,  the 
body  of  which  is  extraordinarily  elongated. 

I.  Smooth,  N on- striated,  or  Involuntary  Muscle. — The  tissue  of 
smooth  muscle  consists  of  contractile  fiber-cells,  spindle-shaped,  cylin- 
drical, or  slightly-flattened  elements  with  tapering  extremities  (Fig.  38). 


FIG.  38.— Two  SMOOTH  MUSCLE-FIBERS  FROM  THE  SMALL  INTESTINE  OF  A  FROG.  X  240.  Isolated  in 
35  per  cent,  potash-lye.  The  nuclei  have  lost  their  characteristic  form  through  the  action  of  the 
lye.  Techn.  No.  26. 

They  vary  in  length  from  45  to  225  <).,  in  width  from  4  to  7  //. ;  in  the 
gravid  uterus  fibers  measuring  0.5  mm.  have  been  found.  They  are  com- 
posed of  a  homogeneous  protoplasm  *  and  an  elongated,  elliptical,  or  rod- 


*The  protoplasm  of  certain  fibers,  those,  for  example,  .of  the  cluctus  deferens,  exhibits 
longitudinal  striation,  which  has  led  some  authors  to  regard  the  smooth  muscle-fiber  as  com- 
posed of  minute  contractile  fibrillae.  In  fishes  and  amphibians  muscle-fibers  containing  pigment 
have  been  found  in  the  iris. 


TISSUES.  9 1 

shaped  nucleus  ;  the  latter  is  characteristic  of  the  smooth  muscle-fiber. 
[Some  authors  add  that  the  smooth  muscle-fiber  is  invested  by  an 
exceedingly  delicate,  structureless,  hyaline  sheath,  corresponding  to  the 
sarcolemma  of  the  striated  fiber.]  The  smooth  muscle-fibers  sometimes- 
lie  scattered  in  the  connective  tissue,  sometimes  are  united  in  complexes. 


End  of  a  muscle-fiber.  Nerve-cell. 

FIG.  39. — INTERCELLULAR-BRIDGES  OF  SMOOTH  MUSCLE-FIBERS.    From  a  longitudinal  section  of  the 
circular  layer  of  the  small  intestine  of  a  guinea-pig.     X  420.    Techn.  No.  26  b. 

In  the  latter  case  they  are  very  firmly  secured  to  one  another  by  delicate 
thorn-shaped  intercellular_-bridges  (Fig.  39  and  Fig.  40,  A).  Septa  of 
connective  tissue  occur  only  at  wider  intervals  (Fig.  40,  B). 

The  fasciculi  are  united  to  form  strata  or  membranes  in  which  their 
disposition  is  parallel,  as  in  the  muscular  coat  of  the  intestine,  or  they 


Connective-tissue  — 
septum. 


Nucleus. 

Smooth  muscle-fibers 
and  nuclei  in  trans- 
verse section. 

FIG.  40  A. — INTERCELLULAR   BRIDGES.    From    a  FIG.  40  B. — SECTION  OF  THE  CIRCULAR  LAYER  OF 

cross-section  of  the  longitudinal  muscular  layer  THE  MUSCULAR  COAT  OF  THE   HUMAN   INTES- 

of  the  large  intestine  of  a  rabbit.    X  600.    Techn.  TINE.     X  560.     The  intercellular  bridges  cannot 

No.  26  b.  be  seen.     Techn.  No.  103. 


cross  and  interlace,  forming  complicated  networks,  as  in  the  urinary 
bladder  and  the  uterus.  The  larger  blood-vessels  run  in  the  connect- 
ive-tissue septa,  the  capillaries  penetrate  the  fasciculi,  within  which 
they  form  networks  with  elongated  meshes.  The  lymph-vessels 
follow  the  course  of  the  blood-vessels  and  are  present  in  consider- 
able numbers. 


92  HISTOLOGY. 

For  the  nerves  of  smooth  muscle,  see  the  Peripheral  Nerve- 
endings. 

Smooth  muscle-tissue  occurs  in  the  alimentary  canal,  in  the  trachea 
and  bronchial  tubes,  in  the  gall-bladder,  in  the  capsule  and  pelvis  of  the 
kidneys,  in  the  ureters  and  the  urinary  bladder,  in  the  reproductive 
organs,  in  the  vascular  channels  and  lymph-vessels,  in  the  eye,  and  in 
the  skin.  The  contraction  of  smooth  muscle-fiber  is  slow  and  not  under 
the  control  of  the  will. 

2.  Striated  or  Voluntary  Muscle. — It  is  only  by  the  study  of  their 
development  that  the  striated  muscle-fibers  are  recognized  as  the  mor- 
phologic equivalents  of  cells.  By  a  colossal  growth  in  length,  by  pro- 
liferation of  their  nuclei,  and  by  peculiar  differentiation  of  their  proto- 
plasm, the  embryonal  elements  have  become  highly  specialized  structures. 
The  fibers  are  cylindrical  in  form  and  in  the  interior  of  the  larger  mus- 
cles have  rounded  or  pointed  ends  ;  at  the  extremities  of  the  muscle 
they  possess  a  pointed  inner  end  and  a  broad  outer  end,  in  contact  with 
the  tendon  ;  the  outer  end  is  blunt  or  notched,  often  step-like  and  tapering. 
Anastomoses,  divisions,  and  fissures  occur  ;  branched  fibers  are  found  in 
the  muscles  of  the  eye,  the  tongue,  and  the  skin  (Fig.  42,  <£).  They  vary 
in  length  from  5.3  to  12.3  cm.,  in  width  from  10  to  100  /*.  It  is  proba- 
ble that  there  are  fibers  having  greater  length,  but  their  isolation  entire  is 
very  difficult  to  accomplish.  In  the  embryo  the  fibers  differ  little  in 
width,  but  after  birth  their  development  in  this  dimension  varies  and  is 
dependent  on  the  functional  activity  of  the  muscle  ;  in  the  adult,  robust 
muscles  possess  thick  fibers,  delicate  muscles  have  thin  fibers.  Apart 
from  this,  their  diameter  depends  on  the  nutritional  condition  of  the  indi- 
vidual. Furthermore,  large  animals  possess  thicker  fibers  than  smaller 
ones.  Hence  the  difference  in  caliber  may  be  of  a  threefold  nature. 

Under  the  microscope  each  fiber  exhibits  alternate  broad  dim  and 
narrower  clear  transverse  striae.  The  substance  of  the  dim  stripes  is 
doubly  refracting  or  anisotropic,  that  of  the  light  stripes  singly  refracting 
or  isotrppic'  High  amplification  shows  that  each  transverse  disc  is 
transversely  divided  ;  invariably  in  the  clear  zone  a  dim  line  may  be 
seen,  the  intermediate  disc,  and  above  and  below  this  a  dark  band,  the 
accessory  disc,  or  secondary  disc.  In  the  anisotropic  (dim)  band  a  clear 
stripe,  the  median  disc,  has  been  observed.  Owing  to  their  extreme 
variation  and  their  instability,  these  discs  are  of  subordinate  significance. 
Besides  the  cross-marking,  a  more  or  less  distinct  longitudinal  striation 
may  be  observed.  Treatment  with  chromic-acid  solutions  renders  this 
striation  more  evident  and  even  causes  the  muscle-fiber  to  fall  apart  into 
delicate  longitudinal  fibrils,  each  of  which  exhibits  the  cross-striae 


TISSUES.  93 

These  fibrils  are  the  contractile  structural  elements  of  the  muscle-fiber* 
and  are  called  ultimate  fibrilUe.  They  are  grouped  into  bundles,  the 
sarcostylcs  or  muscle-columns,  in  which  they  are  arranged  parallel  to  one 
another  and  held  together  by  the  sarcoplasm,  which  also  surrounds  and 
unites  the  neighboring  bundles.  The  disposition  of  the  sarcoplasm  is 
best  seen  in  cross-section  ;  high  amplification  is  required.  It  presents 
the  appearance  of  a  clear  network,  within  the  meshes  of  which  are  the 
muscle-columns  in  section, — small,  dark,  polygonal  areas  known  as 
Cohtiheim's  fields.  The  sarcoplasm  contains  the  interstitial  granules — 
consisting  partly  of  fat  and  probably  also  partly  of  lecithin — and  the 
nuclei.  The  latter  are  oval  bodies  placed  parallel  to  the  long  axis  of  the 


FIG.  41. — B.  PORTION  OF  MUSCLE-FIBER  OF  MAN  ;  a,  anisotropic,  *',  isotropic  band  ;  q,  intermediate 
disc;  £,  nucleus.  X  560.  Techn.  No.  20  b.  A.  MUSCLE-FIBER  OF  FROG;  f,  fibrillae;  k,  nucleus. 
X  240.  Techn.  No.  23. 

muscle-fiber ;  in  mammals,  bony  fishes,  and  some  birds  they  are  chiefly 
situated  immediately  beneath  the  sarcolemma,  upon  the  surface  of  the 
muscle-substance  ;  in  other  vertebrates  they  are  embedded  within  the 
sarcoplasm. 

Each  muscle-fiber  is  closely  invested  by  a  structureless  sheath,  the 
sarcolemma,  which  represents  the  cell-membrane.  Therefore  the  fiber 
of  striated  muscle  consists  of  fibrillae,  sarcoplasm,  muscle-nuclei,  and 
sarcolemma. 

The  striated  fibers  are  found  in  the  muscles  of  the  trunk  and  the 
extremities,  of  the  eye  and  the  ear,  also  in  the  tongue,  the  pharynx, 
the  upper  half  of  the  esophagus,  the  larynx,  the  diaphragm,  the  genital 
organs,  and  the  rectum. 

*  The  muscle-fibers  of  some  animals,  after  treatment  with  certain  reagents,  cleave  trans- 
versely into  discs.  Fibrillae  and  discs  may  be  further  separated  into  smaller  prismatic,  aniso- 
tropic particles  called  sarcoits  elements.  Certain  authors  have  interpreted  the  discs,  others  the 
sarcous  elements,  as  the  true  structural  units. 


94 


HISTOLOGY. 


In  some  animals,  the  rabbit,  for  example,  two  varieties  of  striated 
muscles  are  distinguished,  the  red  (semitendinosus,  soleus)  and  the 
white  or  pale  (adductor  magnus)  ;  and  correspondingly,  two  varieties  of 
muscle-fibers  :  I ,  dim  fibers,  rich  in  sarcoplasm,  less  regularly  cross- 
striped,  exhibiting  more  distinct  longitudinal  striation,  possessing  in 
general  a  smaller  diameter  (for  example,  those  forming  the  soleus  of  the 
rabbit)  ;  2,  pale  fibers,  poor  in  protoplasm,  more  distinctly  cross-striated, 
having  in  general  a  greater  diameter.  The  latter  represent  the  more 
highly  differentiated  muscle-fibers.  While  in  certain  animals  the  two 
varieties  of  fibers  occur  separately,  each  in  particular  muscles,  in  others 
— also  in  man — they  are  found  intermingled  in  the  same  muscle.  As  a 


FIG.  42.— PORTIONS  OF  ISOLATED  STRIATED  MUSCLE-FIBERS  OF  FROG.  X  50.  i.  After  treatment  with 
water ;  s1,  sarcolemma  ;  at  ;r  the  muscle-substance  is  torn,  the  cross-striation  not  apparent,  the  longi- 
tudinal striation  distinct.  Techn.  No.  21.  2.  After  treatment  with  acetic  acid:  k,  nuclei;  the  fine 
stippling  represents  the  interstitial  granules.  Techn.  No.  22.  3.  After  the  action  of  concentrated 
potash  solution;  ^,  rounded  ends;  the  numerous  nuclei  are  swollen  and  vesicular  in  appearance. 
With  this  amplification  the  cross-striation  in  2  and  3  is  not  visible.  Techn.  No.  24.  4.  Branched 
muscle-fiber  from  the  tongue  of  frog. 


rule,  the  more  functionally  active  muscles,  the  cardiac,  ocular,  masti- 
catory, and  respiratory,  contain  the  greater  number  of  red  fibers.  The 
pale  fibers  contract  more  rapidly,  but  are  sooner  fatigued. 

The  contraction  of  the  striated  fibers,  compared  with  that  of  smooth 
muscle-fibers,  is  rapid  and  is  under  the  control  of  the  will.  The  striated 
fibers  are  united  into  bundles  by  fibrillar  connective  tissue,  which  serves 
also  to  convey  the  numerous  ramifications  of  the  blood-vessels  and 
nerves  supplying  the  muscular  tissue.  The  lymphatic  vessels  are  few  in 
number. 

3.  Cardiac  Muscle. — The  muscle-fibers  of  the  heart  occupy  a  pecu- 
liar position.  Although  transversely  striated,  in  the  history  of  their 
development,  as  well  as  histologically,  they  must  be  regarded  as  modifi- 


TISSUES. 


95 


cations  of  the  smooth  muscle-fibers.  In  the  lower  vertebrates,  in  frogs, 
for  example,  they  are  spindle-shaped  fibers  possessing  elongated  nuclei, 
that  often  are  more  distinctly  striated  transversely  than  longitudinally 
(Fig.  43,  A). 

The  cardiac  muscle-fibers  of  mammals  are  short  cylinders,  the  ends 
of  which  often  are  step-like.  The  protoplasm  is  partially  differentiated 
into  cross-striated  fibrilUe,  which  not  infrequently  are  grouped  into  muscle- 
columns  radially  arranged  to  the  axis  of  the  fiber  (Fig.  43,  D).  The 
remnant  of  undifferentiated  protoplasm,  the  sarcoplasm,  proportionately 
considerable  in  comparison  with  that  of  striated  voluntary  fibers,  is  found 
chiefly  in  the  axial  part  of  the  fiber,  from  which  processes  radiate  between 
the  muscle-columns.  Owing  to  the  generous  amount  and  to  the  dispo- 


Muscle- 
cohunns. 


Sarcoplasm. 


FIG.  43.—  A  and  JS,  MUSCLE-FIBERS  OF  HEART,  isolated  in  potash-lye.  A.  Of  frog.  B.  Of  rabbit; 
x,  lateral  branches.  X  240.  Techn.  like  Xo.  24.  C,  from  a  longitudinal  section,  D,  from  a  cross- 
section  of  a  papillary  muscle  of  man.  C  magnified  240,  D  560,  diameters.  Techn.  No.  35. 

sition  of  the  sarcoplasm,  longitudinal  striation  is  often  marked.  The  oval 
nucleus  is  embedded  in  the  axial  part  of  the  sarcoplasm,  which  frequently 
contains  pigment-granules  or  oil-droplets.  A  cell-membrane  or  sarco- 
lemma  is  wanting.  The  cardiac  muscle  of  the  higher  animals  is  charac- 
terized by  the  anastomosis  of  the  cells  by  means  of  short,  oblique  or 
transverse,  lateral  processes.  [The  cells  are  joined  end  to  end,  transverse 
lines  of  cement-substance  indicating  the  line  of  union  between  the  indi- 
vidual elements.] 

TECHNIC. 

No.  20. — Striated  Muscle-fibers  ;  a  (of  the  frog). — With  the  scissors 
placed  flat  and  parallel  to  the  course  of  the  fibers,  cut  a  piece  about  I  cm. 
long  from  the  adductor  muscle  of  a  recently-killed  frog.  Take  a  frag- 
ment from  the  inner  surface  of  this  piece  and  tease  it  in  a  small  drop  of 
salt  solution,  add  a  second  larger  drop  of  the  same  liquid  and,  without 


g  HISTOLOGY. 

pressing,  cover  the  preparation  with  a  cover-glass.  With  low  magnifica- 
tion (50  diameters)  the  cylindrical  form,  the  difference  in  thickness, 
occasionally  also  the  cross-striation  of  the  isolated  fibers  may  be  seen 
(Fig.  42).  With  higher  magnification  (240  diameters)  the  cross-striation 
is  distinctly  seen,  and  occasionally  pale  nuclei  and  refracting  granules. 
The  presence  of  numerous  granules  within  the  muscle-fibers  is  probably 
an  indication  of  active  metabolic  processes.  Where  the  muscle-fibers  are 
cut  across,  the  muscle-substance  not  infrequently  protrudes  from  the 
sarcolemma. 

b  (Of  maii). — I  have  found  beautiful  striated  fibers  in  muscles  taken 
from  the  human  cadaver  injected  with  carbolic  acid. 

To  preserve,  stain  under  the  cover-glass  with  picrocarmine  (p.  48) 
for  about  five  minutes,  then  displace  the  staining  fluid  with  diluted 
glycerol. 

No.  21. — The  Sarcolemma. — Treat  preparation  No.  20  a  with  a 
couple  of  drops  of  ordinary  water.  In  from  two  to  five  minutes  it  will  be 
seen,  with  the  low  power  (50  diameters),  that  the  sarcolemma  is  raised 
from  the  muscle-substance  in  the  form  of  transparent  blebs  ;  at  some 
places,  where  the  torn  muscle-substance  has  retracted,  the  sheath  ap- 
pears as  a  delicate  line  spanning  the  interval  (Fig.  42,  I,  s  s'). 

No.  22. — Muscle  Nuclei. — Prepare  muscle-fibers  after  No.  20  a ; 
treat  them  with  a  drop  of  acetic  acid  (p.  48).  The  shrunken  but  sharply- 
outlined  nuclei,  with  the  lower  power,  have  the  appearance  of  spindle- 
shaped  streaks  (Fig.  42,  3). 

No.  23. — Fibrillce. — Place  the  fresh  muscle  of  a  frog  in  20  c.c.  of 
O.  I  per  cent,  chromic-acid  solution  (p.  30).  In  about  twenty-four  hours 
the  tissue  may  be  teased  in  a  drop  of  water  and  fibers  will  be  found,  the 
ends  of  which  have  separated  into  their  ultimate  fibrillae  (Fig.  41,  A).  If 
it  is  desired  to  make  a  permanent  preparation,  place  the  muscle  in 
water  for  one  hour,  then  in  20  c.c.  of  33  per  cent,  alcohol,  ten  or  twenty 
hours  ;  tease  at  once  or  preserve  in  70  per  cent,  alcohol  until  wanted  and 
then  isolate  (p.  28).  If  the  chromic  acid  be  removed  by  allowing  the 
tissue  to  remain  in  alcohol  (frequently  renewed)  for  several  weeks,  the 
teased  preparation  may  then  be  stained  with  picrocarmine  in  the  moist 
chamber  and  this  replaced  by  glycerol  (p.  49).  Beautiful  fibrillae  can  also 
be  obtained  by  teasing  the  muscles  of  larval  salamanders  that  have  been 
fixed  according  to  Techn.  No.  I  and  stained  in  bulk  in  borax-carmine 
(P-  37). 

No.  24. — The  Ends  of  the  Muscle-fibers. — Place  the  fresh  gastroc- 
nemius  muscle  of  the  frog  in  20  c.c.  of  concentrated  potash-lye,  and 
cover  the  watch-glass.  In  from  thirty  to  sixty  minutes  (in  a  cold  room, 
somewhat  later)  the  muscle,  if  lightly  moved  with  a  glass-rod,  falls  into 
its  fibers.  Should  this  fail,  the  solution  is  not  strong  enough  (see  p.  29). 
Transfer  a  number  of  the  fibers  in  a  drop  of  the  same  solution  to  a  slide 
and  carefully  apply  a  cover-glass.  With  the  low  power  the  ends  of  the 


TISSUES.  97 

muscle-fibers  and  numerous  nuclei  may  be  seen  (Fig.  42,  3).  The  fibers 
should  not  be  examined  in  water  or  glycerol  since  the  lye  thus  diluted 
soon  destroys  them. 

No  25. —  /> 'ranched  Muscle-fibers. —  Remove  the  tongue  from  a 
recently-killed  frog  (it  is  attached  in  front  to  the  lower  jaw,  is  free  behind) 
and  place  it  in  20  c.c.  of  pure  nitric  acid,  to  which  about  5  gm.  of  potas- 
sium chlorate  have  been  added  (some  undissolved  chlorate  must  remain 
in  the  bottom  of  the  vessel).  In  a  few  hours,  with  glass-rods  carefully 
transfer  the  tongue  to  30  c.c.  of  distilled  water,  which  must  be  frequently 
changed.  In  this  the  tissue  can  remain  a  week,  though  it  may  be  used 
at  the  end  of  twenty-four  hours.  For  this  purpose  put  it  in  a  test-tube 
half  filled  with  water  and  shake  it  several  minutes  ;  the  tongue  will  fall 
to  pieces.  Turn  the  contents  of  the  test-tube  into  a  capsule  and  in  an 
hour  or  later  place  a  little  of  the  sediment  that  has  been  deposited  in  the 
meanwhile  in  a  drop  of  water  on  a  slide.  The  tissue  may  be  further 
isolated  with  the  teasing  needles,  but  in  most  cases  this  is  superfluous. 
Examine  with  the  low  power.  Stain  under  the  cover-glass  with  picro- 
carmine  (p.  48).  Mount  in  dilute  glycerol  (p.  22).  (Fig.  42,  4.) 

Xo.  26. — (a)  SmootJi  Muscle-fibers. — These  are  best  isolated  by 
placing  a  piece  of  the  stomach  or  intestine  of  a  frog  just  killed  in  20  c.c. 
of  potash  solution  and  treating  like  No.  25  (Fig.  38). 

(U)  Intercellular  Bridges. — Take  from  a  guinea-pig yksT*  killed  a  piece 
of  the  small  intestine  from  i  to  2  cm.  long,  fix  it  in  100  c.c.  of  Zenker's 
fluid  (p.  31),  harden  it  in  gradually-strengthened  alcohol  (p.  33),  and 
stain  the  sections  with  safranin  (p.  25).  The  bridges  can  only  be 
distinctly  seen  in  very  thin  sections  (5  P-  thick)  prepared  with  the  micro- 
tome (see  Paraffin  Embedding,  Microtome  Technic). 


IV.    THE  NERVOUS  TISSUES. 

The  elements  of  the  nervous  tissues,  in  an  early  embryonic  stage, 
are  without  exception  cells  having  a  spherical  form,  the  so-called 
ucuroblasts.  In  the  course  of  development  they  become  elongated  and 
pyriform  ;  the  narrow  part  grows  out  as  a  long,  delicate  process,  often 
extending  the  length  of  a  meter,  and  terminates  in  a  free,  branched  end  ; 
it  is  named  nerve-process.  From  the  body  of  the  cell,  now  termed  a 
nerve-  or  ganglion-cell,  other  processes  may  arise,  which,  however,  are 
short  and  divide  dichotomously  ;  they  are  called  dcndrites,  or  protoplasmic 
processes.  Delicate  lateral  branches,  the  collateral  fibers,  may  grow 
from  the  nerve-process.  The  nerve-cell  and  nerve-process  together  form 
an  individual  element,  the  neuron  (neurodendron).  The  dendrites  and 
collateral  fibers  are  to  be  regarded  as  secondary  processes  of  the 
neuron. 
7 


98 


HISTOLOGY. 


—     Neurilemma. 


^Dendrites. 


—  Nerve- 
process. 


Collateral  branch. 


Medullary  sheath. 


Axis-cylinder. 


;  Terminal  branches. 


FIG   44. — DIAGRAM  OF  A  NEURON. 


The  nerve-process  may  remain 
naked  throughout  its  course,  or  it 
may  receive  different  sheaths ;  these 
are  the"  newilemma,  or  sheath  of 
Schwann,and  the  medullary  sheath.* 
Both  invest  the  nerve-process  only 
in  a  portion  of  its  course.  There 
are  stretches  in  which  the  axis- 
cylinder  is  entirely  without  invest- 
ment, is  naked  (Fig.  44,  a)  ; 
stretches  in  which  it  is  enveloped 
only  by  the  neurilemma  (Fig. 
44,  H)  or  only  by  the  medullary 
sheath  (Fig.  44,  r),  and,  finally, 
stretches  in  which  both  sheaths 
are  present  (Fig.  44,  d)\  m  this 
case  the  medullary  sheath  is  always 
the  innermost  envelope,  lies  directly 
upon  the  cylindrical  nerve-process, 
and  is  itself  ensheathed  by  the 
neurilemma.  The  nerve-process 
always  occupies  the  longitudinal 
axis  ;  hence  the  name,  axis-cylinder. 
Owing  to  the  often  great  length 
of  the  nerve-process,  it  is  not 
possible  to  investigate  the  neuron 
as  a  whole.  As  a  rule,  it  is  seen 
only  in  fragments,  either  the  nerve- 
cell  or  the  nerve-process,  and 
this  explains  the  former  division 
of  the  elements  of  the  nervous 
tissues  into  nerve-cells  and  neri'c- 
fibcrs,  the  latter  being  the  nerve- 
processes  with  their  sheaths.  There 
are  no  independent  nerve-fibers, 
each  so-called  fiber  is  a  process 
of  a  nerve-cell  ;  if  the  connec- 
tion between  the  fiber  and  the 


*  The  neurilemma  is  a  product  of  connective  tissue ;  the  origin  of  the  medullary  sheath 
requires  further  investigation  ;  it  is  probable  that  the  nerve-process  and  the  nutritive  fluid  sur- 
rounding it  play  a  part  in  its  formation. 


TISSUES. 


99 


cell  is  broken,  the  fiber  dies  cellulifugahvard  from  the  point  of  solution 
of  continuity.      For  practical  reasons  the  old  classification  is  retained. 


NERVE-CELLS. 

Nerve-cells  (ganglion-cells)  are  found  in  the  ganglia,  in  the  organs 
of  special  sense,  along  the  course  of  cerebro-spinal,  as  well  as  sympa- 
thetic nerves,  but  principally  in  the  central  nervous  system.  They  differ 
greatly  in  size  (4  to  135  ,a  and  more)  and  in  form.  There  are  spherical 
and  spindle-shaped  nerve-cells,  and  irregularly-stellate  forms  are  very 
common  ;  the  latter  are  those  in  which  the  protoplasm  sends  off  several 
processes  and  so  gives  rise  to  the  stellate  outlines.  Nerve-cells  having  two 
processes  are  termed  bipolar,  those 
having  several  processes,  multipolar 
ganglion-cells  (Fig.  45  and  Fig. 
46).  There  are  also  unipolar  r\£YVQ- 
cells;  these  occur  in  the  sympathetic 
nerve  of  amphibians  and  universally 
in  the  olfactory  mucous  membrane. 
They  possess,  in  fact,  but  a  single 
process.  The  nerve-cells  of  the 
spinal  ganglia,  on  the  other  hand, 
are  only  apparently  unipolar ;  bi- 
polar in  the  embryo,  in  the  course 
of  development  they  become  uni- 
polar by  the  gradual  approach  of 
the  processes,  which  eventually 
come  off  from  the  cell  by  a  com- 
mon stalk,  from  which  they  then 
diverge  at  right  or  obtuse  angles. 

These  are  the  cells  described  as  having  T-shaped  or  Y-shaped  processes. 
Apolar  cells,  that  is,  nerve-cells  without  processes,  are  either  immature 
forms  or  artificial  products,  the  processes  in  the  latter  case  having 
been  torn  off  in  the  manipulation  required  for  isolation. 

Each  nerve-cell  consists  of  a  granular  or  faintly-striated  protoplasm,* 
that    not   infrequently   contains    pigment-granules,   and    of  a    vesicular 


FIG.  45.— VARIOUS  FORMS  OF  NERVE-CELLS. 
X  240.  i,  Bipolar  cell  from  the  ganglion 
acusticum  of  an  embryo  rat.  Techn.  No.  187. 
2,  Multipolar  cell  from  the  spinal  cord  of  man. 
Techn.  No.  28.  3,  Cell  from  the  Gasserian 
ganglion  of  man,  axis-cylinder  process  torn 
off.  Techn.  No.  27.  4,  Cell  with  T-branches 
from  a  spinal  ganglion  of  a  young  rat.  Techn. 
No.  70. 


*The  minute  structure  of  the  protoplasm  differs  in  the  different  kinds  of  nerve-cells;  for 
example,  the  motor-cells  of  the  anterior  horn  of  the  spinal  cord,  besides  pigment,  possess  deeply 
staining  masses,  the  so-called  chromopJiilic  granules,  that  extend  into  the  beginning  of  the 
demlrites,  but  not  into  the  nerve-process.  The  protoplasm  of  the  cells  of  the  spinal  ganglia,  on 
the  other  hand,  exhibits  delicate  filaments,  that  are  in  connection  with  granules. 


100 


HISTOLOGY. 


nucleus  poor  in  chromatin,  that  encloses  a  conspicuous  nucleolus.      This 
nucleus  is  characteristic  for  nerve-cells.      A  cell-membrane  is  wanting. 

The  processes  of  nerve-cells  are  of  two  kinds  :  I ,  the  nerve-process 
(axis-cylinder,  axon)  and,  2,  the  branched  protoplasmic  processes  (den- 
drites).  (Fig.  46  and  Fig.  47.)  They  are  most  readily  distinguished  in 
the  multipolar  cells.  The  nerve-process,  usually  the  only  process  of  the 
kind,*  is  the  first  outgrowth  from  the  embryonal  spherical  cell  and  is 
characterized  by  its  hyaline  appearance  and  smooth  outlines  ;  its  course 
is  cellulifugal — it  leads  from  the  cell.  The  protoplasmic  processes,  usu- 


FIG.  46.— Two  FORMS  OF  MULTIPOLAR  NF.RVE-CELLS  FROM  THE  VENTRAL  HORN  OF  THE  SPINAL 
CORD  6V  A  NEWBORN  RABBIT,  SHOWING  THE:  RICHLY-BRANCHED  PROTOPLASMIC  PROCESSES. 
n.  Nerve-process.  X  60.  Techn.  No.  70.  (Schaper.) 


ally  several  in  number,  are  a  later  outgrowth  of  the  embryonal  cell,  and 
are  thicker,  granular  or  finely  striated,  and  often  varicose  ;  their  course  is 
cellulipetal — toward  the  cell.  They  undergo  repeated  division  and  finally 
terminate  in  an  intricate  arborization  of  extremely  fine  fibrils  ;  in  this 
way  the  cell  acquires  an  enormous  superficial  enlargement,  which  on  the 
one  hand  exalts  the  sustentative  power,  on  the  other,  the  susceptibility 


*  It  is  said  there  are  cells  with  several  nerve-processes,  Cajal's  cells  in  the  cerebral  cortex. 
In  bipolar  ganglion-cells,  the  two  processes  of  which  become  the  axis-cylinders  of  medullated 
nerve-fibers  (cells  of  the  spinal  ganglia  of  lower  vertebrates  and  of  embryos)  the  central  process 
running  toward  the  central  nervous  system  corresponds  to  the  nerve-process,  the  peripheral 
process  to  a  dendrite. 


TISSUES. 


101 


of  the  cell-body  to  nerve-stimuli — transmitted  by  the  terminal  ramifica- 
tions of  nerve-processes  lying  between  the  fibrils. 

According  to  the  behavior  of  the  nerve-process,  two  kinds  of 
n^rve-cells  are  distinguished,  cells  of  tJie  first  type,  having  a  long  nerve- 
process  which  becomes  the  axis-cylinder  of  a  medullated  nerve-fiber,  and 
cells  of  tJic  second  type,  having  a  short  nerve-process  which  divides  and 
subdivides  and  terminates  in  a  nervous  ramification  in  the  vicinity  of 
the  cell  (Fig.  48).  The  nerve-process  of  cells  of  the  first  type,  after 


Dendrites. 

Cell-body. 


Axis-cylinder  process. 


FIG.  47.— NERVE-CELL  (CKLL   OF   PURKINJE)  FROM  A  SECTION  THROUGH  THE    HUMAN  CEREBELLAR 

CORTEX.     X  180.    Techn.  No.  74. 


giving  off  a  number  of  fine,  branched  twigs,  the  collateral  fibers  (paraxons) 
and  running  an  extended  course,  often  embracing  many  centimeters,  as 
the  axis-cylinder  of  a  nerve-fiber,  undergoes  rapid  division  and  termi- 
nates in  a  plexus  of  delicate  fibrils.  It  is  supposed  that  all  the  processes 
terminate  in  free  endings,  without  forming  anastomoses  ;  accordingly 
there  is  no  connection  between  the  processes  of  adjacent  cells  except  by 


102 


HISTOLOGY. 


contact.     Properly,  therefore,  there  can  be  no  nervous  network,  but  only 

neuropUent). 


a  dense  feltwork  of  interlacing  fibrils 


NERVE-FIBERS. 

Dependent  upon  the  presence  or  absence  of  the  medullary  sheath, 
nerve-fibers  are  divided  into  medullatcd,  or  white,  and  nonmcdnllatcd,  or 
gray.  Each  division  is  susceptible  of  a  subdivision  dependent  on  the 
presence  or  absence  of  the  neurilemma. 

Nerve-cell  of  the  first  type. 


Nerve  cell  of  the 
second  type. 


Axis-cylinder  process- 


FIG.  4.8.—  Two  NERVE-CELLS  FROM  THE  SPINAL  CORD  OF  AN  EMBRYO  CHICK  SEVEN  DAYS  OLD.     The 
axis-cylinder  or  nerve-process  of  the  left  cell  is  not  seen  in  its  entire  length.     X  200.     Techn.  No.  70. 


Nonmedullated  Fibers.  Without  a  Ncnrilcmma. — These  fibers 
consist  of  the  naked  axis-cylinder  alone  and  are  found  in  the  olfactory 
nerves,  where  they  are  held  together  and  grouped  into  bundles  by 
connective  tissue.  Similar  are  many  fibers  of  the  sympathetic  nerve,  the 


*  There  may  be  some  exceptions  ;  in  recent  investigations  of  the  retina  and  of  the  electric 
organ  of  the  torpedo  nervous  networks  formed  by  the  processes  of  several  nerve-cells  have  been 
described.  In  general,  the  phrase  "  nervous  network  "  or  "  nervous  plexus"  is  to  be  interpreted 
as  signifying  the  disposition  of  single  nerve- fibers  that  branch  off  from  nerve-fiber  bundles  to 
join  other  bundles.  The  transition  of  one  nerve-fiber  into  another  never  occurs. 


TISSUES. 


103 


so-called  Remak  s  fibers  ;  *  they  are  transparent,  cylindrical  or  band-like 
in  form,  from  3  to  7  p.  wide,  about  2  /j.  thick,  and  exhibit  faint 
longitudinal  striation  ;  they  are  similarly  grouped  into  bundles,  which 
possess  an  imperfect  sheath,  formed  by  closely  applied,  flattened 
connective-tissue  cells  having  oblong  nuclei,  that  correspond  to  the 
endoneurium  (see  the  chapter  on  the  nervous  system). 

While  the  fibers  so  far  described  exhibit  the  same  structure  through- 
out their  length,  there  are,  on  the  other  hand,  nerve-fibers  of  which  only 
certain  divisions  are  naked  axis-cylinders  ;  such  divisions  occur  as  per- 
ipheral endings  of  the  nerves  of  special  sense,  of  sensory  as  well  as 
motor  nerves  ;  also  the  first  division  of  the  nerve-process  proceeding  from 
the  nerve-cell  is  a  naked  axis-cylinder  (Fig.  44,  a). 

Nonmedullated  Nerve-fibers.     With  a  Neurilemma. — These  con- 
sist of  the  axis-cylinder  enveloped  by  a  neurilemma  and  are  of  the  same 
structure    throughout    their     length  ; 
they  are  found  in  many  invertebrates 
and   in   cyclostoma.     They  occur  as 
limited  portions  in  the  course  of  the 
cerebro-spinal  nerve-fibers  (Fig.  44,  /;). 

Medullated  Nerve-fibers.  — 
Among  these  are  no  fibers  that  pos- 
sess the  medullary  sheath  in  their 
entire  length  ;  this  always  invests  only 
one  portion  of  the  axis-cylinder.  The 
medullated  fibers  may  be  without  a 
nciirilciinna,  and  consist  of  the  axis- 
cylinder  and  the  medullary  sheath  ; 
such  fibers  occur  only  in  the  central 
nervous  system.  Medullated  fibers 
with  a  neurilemma  are  found  in  the 
trunks  and  branches  of  the  cerebro- 
spinal  nerves,  also  in  the  sympathetic 

nerve,  and  vary  in  thickness  from  I  to  20  /*.  The  thickness  of  the  nerve- 
fiber  bears  no  relation  to  its  motor  or  sensory  nature,  but  appears  to  be 
determined  by  its  length  :  the  longer  its  course,  the  thicker  is  the  fiber. 
Division  of  the  medullated  fibers  occurs  (i)  throughout  the  central 
nervous  system,  principally  where  the  collateral  fibers  diverge  at  right 
angles  into  the  white  substance  ;  and  (2)  in  the  peripheral  nervous 
system  shortly  before  their  ultimate  distribution  (Fig.  44). 

*  By  Remak's  fibers  some  authors  understand,  not  bundles  of  naked  axis-cylinders,  but 
individual  axis-cylinder  processes  of  sympathetic  ganglion-cells. 


FIG.  49.— TEASED  PREPARATION  OF  THE  SYM- 
PATHETIC NERVE  OF  RABBIT,  i.  Nonmedul- 
lated, 2,  thin  medullated  nerve-fibers;  3, 
ganglion-cell ;  the  large  nucleus  has  lost  its 
characteristic  appearance  in  consequence  of" 
the  treatment  with  osmic  acid ;  4,  nuclei  of 
connective-tissue  capsule  ;  5,  fine  connective- 
tissue  fibers.  X  240.  Techn.  No.  34. 


IO4 


HISTOLOGY. 


The  medullated  nerve-fibers  have  a  brief  lease  of  life.  They 
degenerate  by  a  gradual  breaking  down  of  the  medullary  substance  and 
axis-cylinder  into  a  granular  mass  containing  numerous  nuclei  ;  in  this 
mass  both  parts  are  regenerated,  the  axis-cylinder  probably  by  out- 
growth of  the  axis-cylinder  process  of  the  nerve-cell.  Regarding  their 
finer  structure  and  peculiar  properties,  the  three  constituent  parts  of 
nerve-fibers  comport  themselves  in  the  following  manner  : 

The  axis-cylinder,  the  essential  part  of  every  nerve -fiber,  occa- 
sionally exhibits  a  delicate  longitudinal  striation,  the  indication  of  its 
fibrillar  structure.  Each  fibrilla  represents  a  special  conducting  path 


Axis-  Medullary        Axis-  Nucleus  of 

cylinder.        sheath.        cylinder,      neurilemma. 


FIG.  50.— MEDULLATED  NERVE-FIBERS  FROM  THE  SCIATIC  NERVE  OF  FROG.  X  280.  i,  Normal,  2, 
shrunken,  3,  tortuous  axis-cylinder  ;  4,  node  of  Ranvier;  5,  neurilemma  with  nucleus.  Techn.  No. 
29.  6,  7,  8,  and  9,  Fresh  medullated  nerve-fibers;  10,  post-mortem  distortion  of  medullary  substance  ; 
r,  annular  constriction ;  /,  incisures  of  Lantermann  ;  /,  medullary  segment.  Techn.  No.  29  a. 


and  is  cemented  to  neighboring  fibrillse  by  a  small  amount  of  finely- 
granular  interstitial  substance,  neuroplasm.  [A  delicate,  elastic,  special 
investment  of  the  axis-cylinder,  the  axilemma,  is  described  by  Kiihne. 
By  some  authors  it  is  regarded  as  an  artefact.] 

The  medullary  sheath  is  composed  of  a  semi-fluid,  highly-refract- 
ing, fatty  substance,  the  myelin,  which  imparts  to  fresh  medullated  fibers 
the  appearance  of  glistening  hyaline  cylinders,  homogeneous  throughout, 
the  structure  of  which  can  only  be  perceived  by  the  help  of  reagents. 

In  favorable  conditions  it  may  be  seen  that  the  medullary  sheath  is 
not  continuous,  but  is  divided  at  slightly  irregular  intervals  by  oblique 
incisions  or  clefts  into  small  conical  or  funnel-shaped  pieces,  the  Schmidt- 


TISSUES. 


105 


L'.vitcnnxnn  segments  (medullary  segments,  cylindro-conical  segments), 
which  are  united  by  cement-substance  (Fig.  50,  9).  Kolliker  has  inter- 
preted these  oblique  markings  as  artefacts.  After  treatment  with 
various  reagents,  the  apparently  homogeneous  medullary  substance  of 
fresh  nerve-fibers  in  dying  undergoes  partial  transformation,  and  the 
fibers  exhibit  a  characteristic  double  contour  (thence  the  old  designation, 
"double-bordered,"  or  "dark-edged"  fibers),  and  later  appear  mottled, 
owing  to  the  distortion  of  the  medullary  substance,  which  collects  into 
irregular  spherical  masses  (Fig.  50,  10).  [According  to  Kuhne  and 
Euald  the  medullary  substance  consists  of  two  parts  :  a  reticulum  com- 
posed of  a  resistant  material  resembling  neurokeratin,  which  encloses 
within  its  meshes  the  other  part,  the  myelin. 
Owing  to  the  variability  in  the  appearance  of 
the  network,  other  authorities  regard  it  as 
an  effect  of  the  reagents  employed  to  demon- 
strate it.] 

At  regular  intervals  along  the  medullated 
nerve-fibers  the  medullary  substance  is  inter- 
rupted, so  that  the  axis-cylinder  and  neuri- 
lemma  come  into  contact.  At  these  points 
the  fibers  exhibit  well-marked  annular  con- 
strictions, termed  nodes  of  Ranvier  (Fig.  51)  ; 
they  are  the  localities  where  the  nutritive  fluid 
can  approach  the  axis-cylinder.  These  con- 
strictions occur  in  all  peripheral  medullated 
fibers,  at  intervals  of  from  0.08  mm.  in  thin, 
to  i  mm.  in  thick  fibers,  dividing  them  into 
mtemodal  segments  or  internodes.  In  the 

vicinity  of  the  nodes  the  axis-cylinder  frequently  shows  a  biconical 
enlargement,  probably  due  to  a  local  accumulation  of  neuroplasm. 
After  treatment  with  silver  nitrate,  the  nodes  are  rendered  conspicuous 
by  a  dark  annular  disc  called  the  constricting  band,  produced  by  the 
staining  of  the  cement-substance  collected  at  these  points,  and  by  distinct 
transverse  striae  (Frommann's  lines),  that  appear  on  the  adjacent  parts  of 
the  axis-cylinder.* 

The  neurilemma,  or  sheath  of  Schwann,  is  a  delicate  structureless 
membrane,  against  the  inner  surface  of  which  lie  oval  nuclei  surrounded 
by  a  very  small  amount  of  protoplasm  (Fig.  50,  5). 

The  union  of  the  elements  of  the  nervous  tissues  in  the  peripheral 


FIG.  51.— MEDULLATED  NERVE- 
FIBERS  OF  FROG,  TREATED  WITH 

SILVER  NITRATE  SOLUTION.  X 
560.  i.  At  r,  node  of  Ranvier  ;  a, 
axis-cylinder,  of  which  only  a 
small  extent  is  silvered  ;  b,  biconi- 
cal swelling  displaced  downward 
owing  to  manipulation.  2.  Axis- 
cylinder  with  the  silvered  portion 
in  situ,  at  a.  3.  Axis-cylinder 
with  cross-markings.  Techn. 
No.  33- 


*  These  striae  are  artefacts  ;   for  their  significance,  see  p.  40,  remark 


IO6  HISTOLOGY. 

nervous  system  is  secured  by  means  of  connective  tissue,  which  contains 
the  ramifications  of  the  blood-vessels.  In  the  central  nervous  system 
they  are  supported  and  held  together,  not  only  by  connective  tissue,  but 
by  a  peculiar  form  of  tissue,  the  ncuroglia. 


TECHNIC. 

No.  27. — Ganglion-cells,  fresh. — Tease  a  small  piece  of  the  Gas- 
serian  ganglion  in  a  drop  of  salt  solution  and  stain  under  the  cover-glass 
with  picrocarmine  for  two  minutes  (p.  48).  The  processes  of  the  cells 
usually  tear  off 

The  nerve-cells  of  the  cerebral  and  the  cerebellar  cortex  may  be  pre- 
pared in  the  same  way  ;  the  processes  likewise  are  easily  lost. 

No.  28. — Multipolar  Nerve-cells  of  the  Spinal  Cord. — Remove  with 
the  scissors  as  much  as  possible  of  the  white  substance  of  the  spinal  cord 
of  an  ox  and  place  the  gray  remnant  in  pieces  i  or  2  cm.  in  length 
in  30  c.c.  of  33  per  cent,  alcohol  (p.  20,  c).  After  thirty-six  or  forty- 
eight  hours  transfer  the  pieces  to  20  c.c.  of  undiluted  neutral  carmine 
solution  (p.  24)  for  twenty-four  hours.  The  now  very  soft  pieces  should 
be  transferred  with  the  section-lifter  to  50  c.c.  of  distilled  water,  in  order 
to  wash  out  some  of  the  stain,  and  after  ten  minutes  spread  with  needles 
in  a  thin  layer  on  a  dry  slide.  With  a  little  practice  the  nerve-cells  can 
be  distinguished  by  their  bright-red  nuclei  ;  the  cell-body  and  the  pro- 
cesses are  not  yet  visible.  Let  the  preparation  dry  thoroughly  and 
mount  it  in  damar  (Fig.  45,  2). 

No.  29. — Fresh  Medullated  Nerve-fibers. — Expose  the  sciatic  nerve 
of  a  frog  just  killed,  and  with  delicate  scissors  cut  it  at  the  level  of  the 
popliteal  space  and  about  one  cm.  higher.  Isolate  in  a  drop  of  salt 
solution. 

No.  29  a. — Better  still,  tease  on  a  dry  slide  by  the  "  half-drying  " 
method.  Hold  the  lower  end  of  the  nerve  with  one  needle,  with  another 
needle  separate  the  nerve-bundles  along  half  the  length  of  the  nerve  ;  a 
thin  shining  membrane  will  span  the  interval  between  the  separated 
bundles.  Add  a  drop  of  salt  solution  and  apply  a  cover-glass.  The 
membrane  contains  numerous  isolated  nerve-fibers.  The  manipulation 
must  be  done  very  rapidly  (in  about  fifteen  seconds),  so  that  the  nerve- 
fibers  do  not  become  dry  (Fig.  50,  6,  7,  8,  9). 

No.  30. — Alterations  of  the  Medullary  Sheath. — Treat  No.  29  a  with 
water  (place  a  drop  at  the  edge  of  the  cover-glass  and  let  it  flow  under). 
In  a  few  minutes  the  formation  of  the  myelin  drops  begins  (Fig.  50,  10). 

No.  31. —  The  Axis-cylinder. — Tease  dry  (like  No.  29  a)  and  stain 
with  methylene-blue  (p.  39)  ;  the  nodes  of  Ranvier  stain  first,  and  often 
so  deeply  that  the  axis-cylinder  cannot  be  recognized  there  (Fig.  50,  4). 
The  axis-cylinder  frequently  shrinks  and  becomes  displaced  within  the 


TISSUES. 


ID/ 


Node  of  Ranvier. 
Biconical  enlargement. 


\ 


Axis-cylinder. 


Medullary  sheath. 


Neurilemma. 


medullary  sheath,  or  it  contracts  and  becomes  convoluted  (Fig.  50,  2,  3). 
On  the  addition  of  glycerol  the  medullary  substance  can  no  longer  be 
distinctly  recognized  as  such,  but  the  nuclei  of  the  neurilemma  are 
often  rendered  plainly  visible  (Fig.  50,  5). 

No.  32. — Exhibition  of  the  Axis-cylinder  with  Chromic  Acid. — Expose 
the  sciatic  nerve  of  a  rabbit  recently  killed,  being  careful  not  to  toncJi  it ; 
place  a  match-stick  parallel  to  the  long  axis  of  the  nerve  and  secure  it 
by  means  of  ligatures  at  the  upper  and  lower  ends  ;  cut  the  nerve  on  the 
farther  side  of  each  ligature  and  place  it,  with  the  wood,  in  100  c.c.  of  a 
o.i  per  cent,  chromic-acid  solution  (p.  31). 

In  about  twenty-four  hours  cut  the  ligatures  and  tease  a  piece  of  the 
nerve,  from  0.5  to  I  cm.  long,  separating  it  into  bundles,  not  fibers.  Put 
the  bundles  back  into  the  chro- 
mic-acid solution  ;  after  twenty- 
four  hours  transfer  them  to  50 
c.c.  of  distilled  water,  and  after 
two  or  three  hours  to  30  c.c.  of 
gradually-strengthened  alcohols 
to  harden  (p.  33).  It  is  advan- 
tageous to  leave  the  bundles  for 
a  long  time,  one  to  eight  weeks, 
in  90  per  cent,  alcohol,  as  they 
are  then  more  readily  stained. 
After  the  hardening  is  completed, 
the  bundles  are  to  be  teased  in  a 
drop  of  picrocarmine,  placed  in 
the  moist  chamber,  and,  after  the 

staining  is  completed  (which  according  to  the  length  of  time  the  tissue 
was  allowed  to  harden  in  the  alcohol  requires  from  one-half  to  three 
days),  preserved  in  acidulated  glycerol  (p.  49).  The  nodes  of  Ranvier 
are  not  as  distinct  as  in  fresh  and  in  osmic-acid  preparations,  but  appear 
as  delicate  transverse  lines  (Fig.  52).  The  somewhat  shrunken  axis- 
cylinder  and  the  nuclei  are  stained  a  fine  red.  The  intensity  of  the  color 
depends  on  the  quality  of  the  picrocarmine,  which  unfortunately  varies 
greatly. 

No.  33. — Nodes  of  Ranvier  and  Axis-cylinders. — Add  10  c.c.  of  a 
I  per  cent,  solution  of  silver  nitrate  to  20  c.c.  of  distilled  water.  Kill 
a  frog,  open  the  abdomen  by  a  crucial  incision,  turn  out  the  viscera, 
and  expose  the  nerves  descending  on  either  side  of  the  vertebral  column. 
Wash  out  the  abdominal  cavity  with  distilled  water  and  pour  over  the 
nerves  about  one-third  of  the  silver  solution.  After  two  minutes  carefully 
cut  out  the  delicate  nerves,  put  them  for  a  half-hour  in  the  remainder  of 
the  silver  solution,  and  place  them  in  the  dark.  Then  transfer  them  to 
10  c.c.  of  distilled  water,  in  which  they  may  remain  for  from  one  to 
twenty-four  hours.  If  the  nerves  are  now  examined  in  a  drop  of  water, 
with  the  low  power,  the  endothelial  sheath  of  the  nerve  and  numerous 
pigment-cells  will  be  seen  ;  frequently  a  blood-vessel  lies  along  the  nerve. 


FIG.  52. —  NERVE-FIBER  OF  RABBIT.    X  560. 


IO8  HISTOLOGY. 

On  examination  with  the  high  power,  little  will  be  seen  of  the  nodes  and 
axis-cylinders,  but  if  the  preparation  be  exposed  for  several  hours  to  day- 
light (or  a  few  minutes  to  sunlight)  the  reaction  takes  place  and  the  parts 
mentioned  become  silvered.  The  biconical  swelling  on  the  axisTcylinder 
often  becomes  displaced  in  teasing,  and  is  not  always  readily  found  by  the 
beginner  (Fig.  51). 

No.  34. — Nonmedullated  Nerve-fibers. — Tease  a  portion  of  the 
pneumogastric  nerve  of  a  rabbit  on  a  dry  slide  (No.  29  a),  and  add  a 
few  drops  of  a  0.5  per  cent,  osmic-acid  solution  ;  in  five  or  ten  minutes 
the  medullated  nerve-fibers  become  blackened  (which  may  be  ascertained 
by  examination  with  the  low  power).  Remove  the  osmic-acid  solution 
and  add  a  few  drops  of  distilled  water,  which  should  be  renewed  in  five 
minutes.  In  five  minutes  more  remove  the  water,  add  a  few  drops  of 
picrocarmine,  apply  a  cover-glass,  and  place  in  the  moist  chamber  for  from 
twenty-four  to  forty-eight  hours  ;  then  displace  the  picrocarmine  with 
acidulated  glycerol  (p.  49).  The  tissue  may  be  teased  again  after  the 
staining  is  completed,  which  is  now  more  easily  done  because  the  ele- 
ments are  more  distinctly  seen.  With  high  magnification  the  medullated 
nerve-fibers  appear  blue-black,  the  nonmedullated  pale  gray  and  finely 
striated  longitudinally.  The  sympathetic  nerve  treated  in  the  same  way 
exhibits  more  numerous  nonmedullated  nerve-fibers.  But  this  nerve  is 
somewhat  more  difficult  to  find.  Cut  through  the  greater  cornu  of  the 
hyoid  bone,  also  the  hypoglossal  nerve,  and  push  them  aside  ;  behind  the 
pneumogastric  nerve  lies  the  sympathetic,  which  is  recognized  by  its 
three  or  four  mm.  in  size,  ellipsoidal,  yellowish,  and  transparent  superior 
cervical  ganglion.  If  the  piece  of  the  nerve  lying  close  under  the  gan- 
glion be  teased,  ganglion-cells,  the  majority  of  which  contain  two  nuclei, 
will  be  obtained  ;  it  is  difficult  to  isolate  the  cells  so  that  their  processes 
can  be  seen.  In  Fig.  49,  accidentally,  only  the  more  unusual  uninucle- 
ated  ganglion-cell  is  seen. 


II.  MICROSCOPIC  ANATOMY  OF  THE  ORGANS. 


i.  THE   CIRCULATORY    SYSTEM. 


THE    BLOOD-VESSELS. 

The  blood-vessels  are  composed  of  fibrous  connective  tissue,  elastic 
fibers,  and  smooth  muscle-fibers,  mingled  in  widely  different  proportions 
and  arranged  in  strata  or  tunics.  In  general,  a  uniform  disposition  of 
the  elements  prevails  in  each  tunic  ;  longitudinal  in  the  inner  and  outer, 
circular  in  the  middle  tunic.  An  exception  to  this  occurs  in  the  com- 
plicated structure  of  the  heart  and  in  the  simple  structure  of  the  capil- 
laries. 

THE    HEART. 

The  walls  of  the  heart  consist  of  three  membranes  :  I,  the  endo- 
cardium ;  2,  the  powerfully  developed  muscular  layer,  the  myocardium  ; 
3,  the  epicardium  (visceral  layer  of  the  pericardium). 

The  endocardium  is  a  connective-tissue  mem- 
brane which  contains  smooth  muscle-fibers  and 
numerous  elastic  fibers.  The  latter  are  especially 
well  developed  in  the  auricles,  where  they  form  a 
close-meshed  network  or  are  blended  in  a  fenes- 
trated  membrane  (Fig.  24).  The  free  surface,  that 
directed  toward  the  cavity  of  the  heart,  is  clothed 
with  a  simple  layer  of  irregularly-polygonal  epi- 
thelial- (endothelial)  cells. 

The  muscular  layer  or  myocardium  consists 
of  muscle-fibers  (for  their  structure,  see  p.  95) 
and  a  delicate  perimysium  surrounding  each  ele- 
ment. Numerous  transverse  and  oblique  processes  (see  Fig.  43) 
unite  the  muscle-fibers  into  complexes,  the  arrangement  of  which*  is 
very  complicated.  The  muscle-tissue  of  the  auricles  is  entirely  separate 
from  that  of  the  ventricles.  In  the  auricles  an  outer  transverse  layer 
common  to  both  and  an  inner  longitudinal  layer  independent  in  each  can 

109 


FIG.  53. —CROSS-SEC- 
TION OF  PAPILLARY 
MUSCLE  OF  HUMAN 
HEART.  ;«.  Muscle- 
fibers  in  section  ;  /, 
perimysium  with 
small  deeply-stained 
nuclei ;  z/,  blood-ves- 
sel. X  240.  Techn. 
No.  35- 


I  10 


HISTOLOGY. 


be  distinguished.  In  addition,  numerous  small  bundles  pursue  inde- 
pendent courses  in  other  directions.  The  muscle-tissue  of  the  ventricles 
is  much  more  irregularly  distributed  ;  the  bundles  extend  in  every 
direction,  often  describing  a  figure-of-eight  in  their  course. 

Within  the  compass  of  the  auricles  the  perimysium  contains  elastic 
fibers,  that  are  connected  with  those  of  the  endocardium  and  of  the 
epicardium.  The  muscular  layer  of  the  auricular  appendages  is  poor 
in  elastic  tissue.  Between  the  auricles  and  ventricles  lie  firm  tendinous 
ligaments  intermingled  with  elastic  fibers,  the  amndi  fibrosi,  of  which  the 
right  is  stronger  than  the  left.  Similar  but  less  developed  ligaments 
lie  at  the  arterial  orifices  of  the  ventricles.  Numerous  muscle-fibers  take 
their  origin  in  these  ligaments. 


FIG.  54. — SMALL  ARTERIKS  OF  MAN.  ;',  Nuclei  of  intima,  the  outlines  of  the  cells  are  invisible  ;  »/,  nuclei 
of  circularly-disposed  muscle-fibers  of  media;  a,  nuclei  of  externa.  A,  artery  with  the  sur- 
face in  focus.  B,  artery  with  the  lumen  in  focus  ;  at  m'  the  nuclei  of  the  muscle-fibers  of  the  media 
are  seen  in  optical  section.  C,  small  artery  shortly  before  transition  into  capillaries;  the  media  con- 
sists of  a  few  isolated  muscle-fibers.  X  240.  Techn.  No.  37  a. 

The  epicardium  is  a  connective-tissue  membrane  penetrated  by 
elastic  fibers  and  fat-cells,  which  on  the  outer  surface  is  covered  with  a 
single  stratum  of  squamous  epithelium. 

The  valves  of  the  heart  are  composed  of  fibrous  connective  tissue, 
continuous  with  that  of  the  annuli  fibrosi,  and  their  surfaces  are  clothed 
by  the  endocardium.  They  contain  muscle-fibers,  but  only  in  the 
attached  margin,  and  elastic  fibers,  which  are  especially  abundant  in  the 
nodules  of  the  free  edges  of  the  semilunar  valves. 

The  numerous  blood-vessels  of  the  muscular  wall  of  the  heart  form 
typical  capillary  networks  with  elongated  meshes  (see  the  Organs  of 
Muscular  System).  The  epicardium  and  endocardium,  the  latter  in  its 
deeper  strata,  also  possess  blood-vessels. 

The  lymph-vessels  of  the  heart  are  extremely  numerous.  They 
form  a  comprehensive  system  embracing  all  the  lymph-spaces  in  the 


THE    CIRCULATORY    SYSTEM. 


I  I 


clefts  between  the  muscle-fibers   and   accompany   the   blood-vessels   in 
their  course. 

The  ncrrc-supply  of  the  heart  includes  medullated  nerve-fibers 
derived  from  the  pneumogastric  and  nonmedullated  sympathetic  nerve- 
fibers  from  the  cervical  ganglia  ;  along  their  course  numerous  ganglion- 
cells  occur. 

The  pericardium  consists  of  compact  connective  tissue  intermingled 
with    elastic    fibers,    which  on    its   inner   sur- 
face,    that     directed    toward    the    heart,     is 
clothed    in    a    simple     layer    of     squamous 
epithelium. 


THE  ARTERIES. 

The  walls  of  the  arteries  comprise  three 
coats:  i,  tunica  intima  ;  2,  tunica  media;  3, 
tunica  extern  a  (adventitia).  The  elements 
of  the  tunica  media  are  transversely  disposed,  m 
those  of  the  other  tunics  chiefly  longitudin- 
ally. The  structure  and  thickness  of  these 
coats  vary  with  the  size  of  the  artery.  This 
renders  their  classification  as  small,  medium, 
and  large  arteries  desirable. 

The  small  arteries  include  the  terminal 
branches  shortly  before  their  transition  into 
capillaries.  The  intima  consists  of  elong- 
ated, spindle-shaped  epithelial-cells  and  a 
structureless  elastic  membrane,  the  so-called 
internal  clastic  membrane,  that  in  somewhat 
larger  arteries  assumes  the  character  of  a 
fenestrated  membrane.  The  media  is  formed 
of  a  single  layer  of  circularly  -  disposed 
smooth  muscle-fibers.  The  externa  is  com- 
posed of  longitudinally-disposed  bundles  of 

connective  tissue  and  fine  elastic  fibers.      It  blends  insensibly  with  the 
surrounding  connective  tissue. 

The  arteries  of  medium  size  comprise  all  the  named  arteries  of  the 
body  with  the  exception  of  the  aorta  and  the  pulmonary  artery.  The 
intima  of  these  vessels  has  increased  in  thickness  owing  to  the  interposi- 
tion between  the  endothelium  and  internal  elastic  membrane  of  fibrous 
connective  tissue,  including  flattened  cells  and  networks  of  delicate  elastic 


FIG.  55.— ENDOTHELIUM  OF  A  MES- 
ENTERIC  ARTERY  OF  RABBIT. 
Surface  view.  X  260.  Teclm. 
No.  38. 


I  12 


HISTOLOGY. 


fibers.*  The  media,  in  addition  to  several  superimposed  layers  of 
circularly-arranged  smooth  muscle-fibers,  comprises  wide-meshed  net- 
works of  elastic  fibers.  At  the  inner  boundary  of  the  media  of  some 
arteries  longitudinally-disposed  muscle-fibers  occur  ;  these  are  especially 
well  developed  in  the  subclavian  artery.  The  proportion  of  the  two 
tissues  in  the  different  arteries  is  extremely  variable.  In  the  celiac, 
femoral,  and  radial  arteries  the  muscle-tissue  preponderates  ;  in  the 


Epithelium 


Vasa 

vasorum. 


FIG.  56. — PORTION  OF  CROSS  SECTION  OF-  THE  BRACHIAL  ARTERY  OF  MAN.     X  100.    Techn.  No.  35. 

carotid,  axillary,  and  common  iliac,  the  elastic  tissue  is  in  excess.  The 
externa  has  also  become  stouter.  Thick  elastic  fibers  occur  in  especial 
profusion  at  the  boundary  of  the  media  and  in  many  arteries  form  a 
continuous  layer  designated  the  external  elastic  membrane.  New  elements 
in  the  externa  of  arteries  of  medium  size  are  smooth  muscle-fibers, 
that  appear  in  single,  longitudinally-disposed  bundles  and  never 
form  a  continuous  layer. 

In  the  large  arteries  (aorta   and   pulmonary  artery)  the  epithelial- 


*  This  subendothelial  layer  is  absent  in  the  uterine  arteries  of  young  individuals,  in  the 
celiac,  the  external  iliac,  the  renal,  and  the  mesenteric  arteries. 


THE    CIRCULATORY    SYSTEM.  113 

cells  of  the  intima  are  shorter  and  more  polyhedral  in  outline  than  in 
medium-sized  vessels.  Immediately  beneath  is  the  subendothelial  layer, 
that  consists  of  fibrous  connective  tissue  enclosing  elastic  networks  and 
flattened  cells,  stellate  or  spherical  in  outline.  The  elastic  networks  are 
closer  meshed  the  nearer  to  the  intima  they  lie,  and  finally  pass  into  a 
fenestrated  membrane  corresponding  to  the  internal  elastic  membrane  of 
small-  and  medium-sized  arteries.  The  media  of  the  large  arteries  is 


Epithelium.          _,     _ 

Fibrous  connective  /^~^L<- 
tissue.  -  ^  — 


~-- •'  — 


Bundles  of  smooth        "" -r~   ~ °~ 
muscle-fibers.       —      "  ~^~"^  -^  _ 


Elastic  fibers.    -'  ^-—-^~  -^ 


- 


Elastic  fibers. 


Connective-tissue 
bundles. 


FIG.  57. — FROM  A  CROSS-SECTION  OF  THE  THORACIC  AORTA  OF  MAN.    X  100.    Techn.  No  35 

characterized  by  the  preponderance  of  elastic  tissue  over  the  muscular 
elements.  The  thin  elastic  networks  of  the  media  of  medium-sized 
arteries  are  here  replaced  by  close  networks  of  richly-developed,  broad, 
elastic  fibers  or  by  fenestrated  membranes,  which  alternate  regularly 
with  lamellae  of  smooth  muscle-fibers.  The  elastic  elements,  like  the 
muscle-fibers,  are  circularly  arranged.  The  muscular  lamellae  are 
penetrated  in  an  oblique  direction  by  elastic  fibers  which  connect  all  the 
elastic  elements  of  the  media. 
8 


114  HISTOLOGY. 

The  elastic  membranes  already  occur  in  the  larger  medium-sized 
arteries  ;  they  are  especially  well-marked  in  the  carotids,  which  closely 
approach  in  structure  the  large  arteries.  The  externa  of  large  arteries 
presents  no  essential  peculiarity  and  differs  but  slightly  from  that  of 
medium-sized  arteries.  It  does  not  possess  the  external  elastic  mem- 
brane. In  the  lower  animals  smooth  muscle-fibers  are  present. 

The  foregoing  classification  of  the  strata  of  the  wall  of  the  artery 
corresponds  to  present  usage.  There  is  a  new  proposition  to  regard  as 
intima  simply  the  endothelial  tube  alone,  as  externa  all  that  lies  outside 
of  the  external  elastic  membrane,  the  latter  to  be  reckoned  as  belonging 
to  the  media.  Between  these  two,  then,  lies  the  media,  of  which  the 

Intima.  ^ 

V   1k%  Internal  elastic 

(^     „ membrane  of 

Smooth 

~---.^     muscle- 
/'      fibers. 

Connective 
„-   ,.  . ~    ^  ,,--"'       tissue. 

Externa.  \  -^-  "—• -—  """•     .          '-   ^  -^.    — 


Smooth  muscle-fibers  of  the  externa. 
FIG.  58. — PORTION  OF  CROSS-SECTION  OF  A  VEIN  OF  LIMB  OF  MAN.    X  100.    Techn.  No.  35. 

external  and  internal  elastic  membranes  represent  the  border-lamellae. 
The  subendotheltal  layer  of  the  large  arteries  is  to  be  reckoned  as 
belonging  to  the  media. 

THE  VEINS. 

There  is  no  definite  proportion  between  the  size  of  the  veins  and  the 
thickness  of  their  walls,  and  no  basis  for  a  division  into  groups  as  in  the 
arteries.  The  veins  are  characterized  by  the  preponderance  of  fibrous 
connective  tissue  and  by  the  slighter  development  of  the  muscular 
elements.  As  in  the  arteries,  three  coats  may  be  distinguished.* 

The  intima  consists  of  a  single  layer  of  endothelial  cells,  that  are 
fusiform  only  in  the  smallest  veins,  in  others  are  polygonal  in  form.  In 


*  Owing  to  the  meager  development  of  the  media  some  histologists  have  suggested  that 
only  two  coats  are  present,  tunica  intima  and  tunica  externa,  and  that  the  layers  usually 
regarded  as  tunica  media  belong  to  the  latter. 


THE    CIRCULATORY    SYSTEM.  I  I  5 

veins  of  medium  size,  having  a  diameter  of  from  two  to  nine  mm.,  the 
subendothelial  layer  consists  of  connective  tissue  containing  nucleated 
cells,  that  in  large  veins  (femoral,  popliteal,  superior  cava)  develops  in 
the  form  of  distinct  fibrous  lamellae.  Surrounding  this  is  the  internal 
elastic  membrane,  which  is  structureless  in  small  veins,  in  medium-sized 
and  large  veins  is  represented  by  elastic  networks.  Obliquely  or 
longitudinally-disposed  smooth  muscle-fibers  occur  in  the  intima  of  the 
iliac,  femoral,  saphenous,  and  mesenteric  veins. 


Intima. 


Media. 


Externa.  •! 


Fi(i.  59.— CROSS-SECTION  OF  A  VEIN  OF  A  HUMAN  LIMB.    X  420.    The  elastic  elements  are  stained. 

Teclin.  No.  36. 


The  media  exhibits  great  variation.  It  is  composed  of  circular 
muscle-fibers,  elastic  networks,  and  fibrous  connective  tissue,  and  is  best 
developed  in  the  veins  of  the  lower  extremities  (especially  in  the  poplit- 
eal), less  so  in  the  veins  of  the  upper  extremities,  still  less  in  the  large 
veins  of  the  abdominal  cavity  ;  it  is  absent  in  many  veins  (those  of  the 
pia  and  dura,  of  the  bones,  of  the  retina,  in  the  superior  cava,  and  also 
in  the  veins  proceeding  from  the  capillaries). 


Il6  HISTOLOGY. 

The  usually  well-developed  externa  consists  of  intercrossing  bundles 
of  connective  tissue,  elastic  fibers,  and  longitudinally-disposed  smooth 
muscle-fibers,  that  are  more  highly  developed  in  the  veins  than  in  the 
arteries.  The  adventitia  of  certain  veins  (the  trunk  of  the  portal  and 

the  renal)  possesses  an  almost  com- 
intima.  -— ^    — --—^—^         plete    membrane   of   longitudinally 

Media.   {       --~^^~^^  * 

arranged  muscle-fibers  (rig.  DO). 


Extema  with    cross-  %!v$K%3~  The  valves  of  the    veins   are 

sectioned   longitudi-  (         t«Vi     '?"..••"•'•'•  I  ;/£!  ^> 

I  ,./¥'       folds     of    the     intima    covered   on 

both     surfaces    by    epithelial-cells, 

FIG.  60. — CROSS-SECTION  OF  THE  RENAL  VEIN  OF        .\  ,1  r  j-  i 

MAN.   xso.   Techn.  NO.  35.  that     on    the   surface   directed   to- 

ward    the     vascular     stream     are 

elongated    in    the    direction    of  the  current ;    on    the   opposite    surface, 
toward  the  wall  of  the  vein,  they  are  transversely  elongated. 


THE   CAPILLARIES. 

The  capillaries  establish  the  communication  between  the  arteries  and 
veins.  There  are  a  few  exceptions,  as,  for  example,  in  the  corpora 
cavernosa  of  the  genital  organs.  The  transition  of  the  arteries  into  the 
capillaries  is  effected  by  a  gradual  simplification  of  the  structure  of  the 
vessel- wall  (Fig.  54).  The  media  becomes  steadily  thinner  and  finally  is 
represented  by  a  few  isolated  circularly-disposed  muscle-fibers  occurring 
at  wide  intervals,  that  ultimately  disappear.  The  externa  becomes  cor- 
respondingly attenuated  until  it  consists  of  a  thin  layer  of  connective 
tissue  containing  cells,  that  ultimately  also  vanishes,  so  that  at  last  the  only 
part  of  the  vessel-wall  that  remains  is  the  intima,  the  layers  of  which  are 
likewise  reduced  until  nothing  is  left  but  a  stratum  of  plate-like,  nucleated 
endothelial  cells.  Hence,  the  walls  of  the  capillaries  consist  of  a  simple 
layer  of  endothelial  cells,  the  form  of  which  may  be  most  aptly  com- 
pared with  a  steel  pen  pointed  at  both  ends.  These  cells  are  united  at 
their  edges  by  a  small  amount  of  cement-substance. 

The  capillaries  divide  without  decrease  in  caliber  and  by  anastomosis 
with  neighboring  capillaries  form  networks  differing  widely  in  the  size  of 
the  meshes.  The  closest  meshes  occur  in  the  capillary  networks  of 
secretory  organs,  for  example,  in  the  lung  and  liver  ;  wide-meshed  net- 
works occur  in  the  muscles,  the  serous  membranes,  the  special-sense 
organs.  The  reverse  obtains  in  regard  to  the  caliber  of  the  capillaries  ; 
the  widest  capillaries  are  found  in  the  liver,  the  narrowest  in  the  retina 
and  in  the  muscles. 

Development  of  Capillaries. — Only  the  developmental  processes  in 


THE  CIRCULATORY  SYSTEM.  \\J 

the  post-embryonic  epoch  will  be  considered  here.  A  minute,  conical, 
protoplasmic  mass  appears  on  the  wall  of  an  existing  capillary,  resting 
by  a  broad  base  on  the  latter  and  terminating  in  a  slender,  tapering,  free 
end.*  In  the  further  course  of  development  this  pointed  free  end  unites 
with  another  off-shoot  that  has  arisen  in  the  same  way  from  another  point 
on  the  capillary  wall.  These  formations  are  solid  at  first,  but  gradually 
become  hollow  by  an  extension  of  the  lumen  of  the  capillary,  and  sub- 
sequently the  walls  of  the  new  vessels  become  differentiated  to  endo- 
thelial  cells.  The  development  of  new  capillaries  is  always  consummated 
in  connection  with  existing  capillaries. 

All   medium   and  large   blood-vessels  possess  small   blood-vessels 


FIG.  61. — SURFACE  VIEW  OF  A  PORTION  OF  THE  GRF.ATER  OMENTUM  OF  A  SEVEN-DAY-OLD  RABBIT. 
c,  Blood-capillaries,  some  containing  blood-corpuscles  ;  s,  capillary  sprout  tapering  to  a  free  solid 
point ;  i,  young  capillary,  the  greater  part  of  which  is  hollow,  at  s'  still  solid  ;  k,  nuclei  of  peritoneal 
endothelium.  X  240.  Techn.  No.  40. 

(vasa  vasorum)  that  provide  for  the  nutrition  of  their  walls  ;  they  run 
almost  exclusively  in  the  adventitia  (Fig.  56).  The  intima  always  is 
without  blood-vessels. 

All  blood-vessels  are  furnished  with  nerves,  which  form  a  plexus  of 
medullated  fibers  in  the  media  of  the  arteries  and  veins.  From  these, 
nonmedullated  fibers  arise  which  are  distributed  to  the  muscle- fibers. 
The  capillaries  are  accompanied  by  encircling  networks  of  delicate 
nonmedullated  nerve-fibers.  Many  blood-vessels  are  surrounded  by 
lymph-channels  ;  occasionally  the  lymph-spaces  in  the  adventitia  are  so 
wide  that  they  form  an  ensheathing  sinus  for  the  blood-vessel,  the 
adventitial  or  perivascular  lymph-space. 

*  Such  blind  capillary  sprouts  may  be  hollowed  out  at  an  early  period  ;  corpuscles  that 
happen  to  flow  into  them  disintegrate,  because  they  are  excluded  from  the  circulation  and  the 
interchange  of  gases,  and  fall  into  fragments  that  have  been  erroneously  interpreted  as  hemato- 
blasts;  they  have  no  connection  with  the  true  hematoblasts. 


I  I  8  HISTOLOGY. 

The  glomus  caroticuin  ("  glandula  carotica  ")  is  no  gland,  but  con- 
sists essentially  of  blood-vessels.  The  capillaries  arising  from  the  division 
of  the  single  arterial  vessel  differ  greatly  in  width  and  are  surrounded  by 
numerous  cells  resembling  the  plasma-cells  of  connective  tissue,  that  are 
arranged  in  rounded  groups  forming  the  so-called  secondary  nodules. 
The  many  veins  collect  at  the  periphery  of  the  organ,  that  besides  con- 
tains fibrous  connective  tissue,  isolated  ganglion-cells,  and  conspicuous 
numbers  of  medullated  and  nonmedullated  nerve-fibers.  Similar  in 
structure  is  the  coccygeal  gland  (glomus  coccygeuni),  the  blood-vessels 
of  which  are  characterized  by  hemispherical  evaginations. 

THE  BLOOD. 

The  blood  *  is  a  slightly  clammy,  red-colored  liquid  which  consists  of 
a  fluid  substance,  the  blood-plasma,  and  formed  elements,  the  blood-cells, 

A    '0 

-  -'O 


FIG.  62. — BLOOD-CORPUSCLES  MAGNIFIED  560  TIMES.  A.  Of  man :  1-6,  discoidal  colored  blood-cells;  i, 
seen  with  close  focus;  2,  with  distant  locus;  3  and  4,  viewed  edgewise;  5,  crenated  in  consequence 
of  evaporation;  6,  after  treatment  with  water;  7,  spherical  colored  blood-corpuscle;  8,  colorless 
blood-corpuscle;  9,  blood-platelets.  B.  Of  frog:  10-13,  colored  blood-cells;  10,  fresh,  nucleus  indis- 
tinct ;  ir,  a  few  minutes  later,  nucleus  plainly  visible  ;  12,  seen  from  the  side  ;  13,  after  treatment  with 
water  ;  14,  living,  15,  dead  colorless  blood-corpuscles.  Techn.  No.  41,  43,  44. 

the  blood-platelets,  and  the  elementary  granules.     The  blood-cells  are  of 
two  kinds  :  colored  blood-cells  and  colorless  blood-cells. 

The  colored  blood-cells  are  soft,  flexible,  highly-elastic  elements  and 
possess  smooth,  slippery  surfaces.  In  man  and  in  other  mammals  they 
have  the  form  of  a  flat,  circular  disc,f  slightly  concave  on  each  surface, 
and  therefore  resemble  biconcave  lenses.  Exceptions  occur  in  the  llama 
and  the  camel,  in  which  the  colored  blood-cells  are  oval.  The  average 
diameter  in  man  is  7. 5  /;,  the  thickness  1.5  u..  The  colored  blood-cor- 
puscles of  domesticated  mammals  are  all  smaller  ;  the  largest  are  those 
of  the  dog  (7.3  /;.).  The  colored  blood-cells  consist  of  a  stroma  (proto- 


*  The  elements  of  the  blood  do  not  form  a  tissue,  but  represent  a  loose  union  of  element- 
ary parts,  without  definite  arrangement  of  the  same, — an  aggregation  of  cells. 

f  In  addition,  there  occur  in  human  blood  spherical  colored  blood-corpuscles,  Fig.  62, 
A,  7  ;  they  are  smaller  (5  /z)  and  few  in  number. 


THE  CIRCULATORY  SYSTEM.  lip 

plasm),  the  spaces  of  which  are  filled  with  the  blood-coloring  matter,  the 
hemoglobin.  The  hemoglobin  imparts  to  the  corpuscle  its  yellow  or 
yellowish-green  color.  A  nucleus  and  a  proper  cell-membrane  are 
wanting.  The  colored  blood-corpuscles  of  fishes,  amphibians,  reptiles, 
and  birds  are  distinguished  from  those  of  mammals  by  their  oval,  bicon- 
vex form,  their  generally  greater  size  (22^  long  by  15  /JL  broad  in  the 
frog),  as  well  as  by  the  presence  of  a  round  or  oval  nucleus  ;  in  other 
respects  they  exhibit  the  same  properties  as  those  of  mammals. 

The  white  or  colorless  blood-cells  (leucocytes)  occur  not  only  in  the 
blood  but  also  in  the  lymphatic  vessels,  where  they  are  termed  "  lymph- 
corpuscles."  They  are  also  found  outside  of  the  vessels,  in  bone-mar- 
row, in  masses  in  adenoid  tissue,  scattered  in  fibrous  connective  tissue, 
and  between  epithelial-  and  gland-cells,  where  they  have  wandered  by 
their  power  of  ameboid  movement  ;  therefore  they 
are  also  called  "  wandering  cells."  (C2&  ^^ 

v^*v     fo^C^ 

In  all  cases  the  colorless   blood-cells   consist  of        a<*~"''-b-\g)  c 
a  clammy  protoplasm  and  a  nucleus,   and  are  with-        ||\  *j»)    fS*) 
out   a    cell-membrane.      A    definite    form   cannot  be 

FIG.    63.  —  COLORLESS 

described,   because   during   life   thev  are   enerasred   in        BLOOD-CELLS  OF 

*  &    fc>  MAN.      c.    Cell    with 

ameboid  activity.  In  a  state  of  rest  they  are  xS^T^frNo.1^: 
spherical  (Fig.  63). 

The  size  and  properties   of  the  nucleus  and  protoplasm  have   led 
to  the  following  classification  : 

1.  The  smallest   leucocytes,   measuring  from  4  to  7.5  p.      They 
possess  a  relatively  large  round  nucleus  surrounded  by  a  narrow  zone  of 
protoplasm,  so  small  in  amount  that  it  can  scarcely  be  demonstrated  by 
the  usual  methods  (Fig.  63,  a).     These   are  regarded   as  young  forms  ; 
they  exhibit  little  activity  and  are'  chiefly  found  in  adenoid  tissue. 

2.  Those  of  the  second  variety  have  a  diameter  of  from   7.5   to 
i.o  fJi ;     the  nucleus   is  spherical   or  deeply  cleft — lobulated — and   sur- 
rounded  by   a    larger    amount    of    granular    protoplasm    (Fig.   63,   ft). 
Occasionally  several  disjoined  nuclei  are  present;  the  slender  filaments 
uniting  the  several  parts  of  the  lobulated  nucleus   are   frequently  over- 
looked, which  then  simulates  several  separate  nuclei.     This  form  is  very 
active  ;    the  tabulation  of  the  nucleus  is  in  fact  regarded  as  the  expres- 
sion of  this  activity  ;   77  per  cent,  of  the  leucocytes  of  the  blood  are  of 
this  form. 

3.  The  leucocytes  of  the  third  class  have  a  diameter  of  from   8  to 
14  IL  and  are  characterized   by  their  granular  protoplasm  ;  the  granules 
are  variable  in  quantity  and  react  differently  to  stains.    According  to  their 
affinity  for  acid,  basic,  or  neutral  dyes,  oxyphile,  basophile,  and  neutrophile 


1 2O  HISTOLOGY. 

leucocytes  are  distinguished.  The  granules  are  probably  the  optical  ex- 
pression of  metabolic  processes  and  of  phases  of  progressive  development 
(see  further,  Techn.  No.  42). 

The  determination  of  the  proportionate  number  of,  as  well  as  the 
ratio  between,  the  colored  and  colorless  blood-corpuscles  is  coupled  with 
considerable  difficulty  and  only  approximately-correct  estimates  can  be 
given.  In  man  one  cubic  millimeter  of  blood  contains  about  5,000,000 
colored  corpuscles.  The  white  blood-corpuscles  are  present  in  the  blood 
in  much  smaller  number,  about  one  in  from  300  to  500  colored 
blood-corpuscles. 

The  blood-platelets  are  very  unstable,  colorless,  round  or  oval  discs 
having  a  diameter  from  one-third  to  one-fourth  less  than  that  of  the 
colored  blood-cells  ;  at  times  they  are  present  in  the  blood  in  large 
numbers.*  A  leading  role  in  the  process  of  coagulation  of  the  blood  is 


FIG.  64.  —  i.  Hemin  crystals  of  man  ;  whetstone  forms  on  the  right.     2.  Crystals  of  common  salt.    3.  Hema- 
toidin  crystals  of  man,  magnified  560  times.    4.  Hem 
a,  a  crystal  falling  apart  lengthwise.     Techn.  No.  47. 


ascribed  to  them.  In  animals  that  have  nucleated  colored  blood- 
corpuscles  the  blood-platelets  also  possess  nuclei. 

The  elementary  granules  are  for  the  most  part  fatty  granules  trans- 
ferred from  the  chyle  to  the  blood.  They  are  frequently  observed  in  the 
blood  of  the  lower  mammals,  but  are  not  normally  present  in  the  blood 
of  man. 

After  death,  or  as  a  result  of  changes  within  the  vessel-walls,  the 
blood  under  the  influence  of  two  substances  which  pass  into  solution  in 
the  plasma,  fibrinoplastin  and  fibrinogen,  coagulates,  and  fibrin  is  formed. 
The  coagulated  blood  separates  into  two  parts,  the  clot  and  the  serum. 
The  clot  is  red  and  contains  all  the  colored  blood-corpuscles,  the  majority 
of  the  colorless  blood-corpuscles,  and  the  fibrin,  which  microscopically 
consists  of  a  feltwork  of  fine,  straight,  interlacing  filaments.  Chemically 
fibrin  resembles  glutinous  connective  tissue.  The  supernatant  serum  is 
colorless  and  contains  a  few  colorless  blood-cells. 

*In  I  c.c.  of  human  blood  there  are  said  to  be  200,000  blood-platelets,  a  number  that 
probably  is  below  the  truth,  since  in  the  methods  of  estimating  some  blood-platelets  always 
adhere  to  the  walls  of  the  pipet. 


THE    LYMPHATIC    SYSTEM.  121 

The  coloring  substance  contained  in  the  colored  corpuscles,  the 
hemoglobin,  possess  the  property  of  crystallizing  under  certain  conditions 
and  in  nearly  all  vertebrates  the  crystals  belong  to  the  rhombic  system. 
Their  form  in  the  different  animals  varies  greatly  ;  in  man  it  is  usually 
prismatic.  Hemoglobin  is  readily  decomposed.  One  of  the  decompo- 
sition products  is  hematin,  which  yields  hematoidin  and  hemin.  Crystals 
of  hematoidin  occur  within  the  body  in  old  extravasated  blood,  for 
example,  in  the  corpus  luteum,  and  are  rhombic  prisms  of  orange-red 
color.  The  hemin  crystals,  when  well  developed,  are  rhombic  plates  or 
needles  of  a  mahogany-brown  color  ;  often  they  are  very  irregular  in 
form.  As  a  positive  indication  of  the  presence  of  blood  they  have  a 
legal  relation  of  great  importance  (see  Techn.  No.  47  a). 

Development  of  Colored  Corpuscles. — From  the  earliest  period  of 
embryonic  development  and  during  the  whole  of  life  nucleated  colored 
blood-cells  (hematoblasts,  erythroblasts)  are  found  in  certain  localities 
(see  bone-marrow).  Their  number  fluctuates  and  runs  parallel  with  the 
energy  of  the  blood-forming  processes.  By  indirect  division  they  give 
rise  to  the  nonnucleated  colored  blood-corpuscles,  that  at  first  contain  a 
nucleus,  but  subsequently  lose  it.  As  centers  for  the  formation  of  blood 
in  the  embryo  the  liver  and  later  the  spleen,  in  the  adult  exclusively  the 
bone-marrow,  may  be  mentioned. 


2.    THE   LYMPHATIC    SYSTEM. 

THE  LYMPH-VESSELS. 

The  walls  of  the  larger  lymph-vessels,  from  0.8  to  0.2  mm.  in 
thickness  and  upward,  like  the  blood-vessels,  are  composed  of  three  coats. 
The  intima  consists  of  endothelial  cells  and  a  network  of  delicate  elastic 
fibers  with  elongated  meshes.  The  media  is  formed  of  circularly-disposed 
smooth  muscle-fibers  and  a  few  elastic  fibers.  The-  externa  consists  of 
longitudinally-arranged  bundles  of  connective  tissue,  elastic  fibers,  and 
bundles  of  smooth  muscle-fibers  likewise  disposed  in  a  longitudinal 
direction.  The  walls  of  the  smallest  lymph-vessels  and  of  the  lymph- 
capillaries  are  composed  exclusively  of  extremely  delicate  endothelial 
cells,  that  often  have  sinuous  outlines.  The  lymph-capillaries  are  wider 
than  the  blood-capillaries,  at  frequent  intervals  present  constrictions  and 
dilatations,  and  where  they  branch  are  often  considerably  expanded  ;  the 
networks  they  form  are  more  irregular. 

The  question  of  the  origin  of  the  lymph-vessels  is  not  yet  satisfac- 


122 


HISTOLOGY. 


torily  decided  ;  while  some  authors  are  of  the  opinion  that  tfie  lymph- 
capillaries  form  a  closed  system,  according  to  another  widely-entertained 
view  the  lymph-capillaries  are  open  toward  the  periphery  and  in  direct 
connection  with  the  system  of  intercommunicating  cell-spaces  of  con- 
nective-tissue (juice-canal  system,  p.  86).  These  interfascicular  clefts 
are  by  some  set  apart,  as  "  lymph-canaliculi,"  from  the  lymph-vessels 
with  well-defined  walls  composed  of  continuous  layers  of  cells  ;  other 
authors  include  the  lymph-canaliculi  among  the  lymph-vessels. 

According   to  the   first  opinion   the  nutritive   fluids    (tissue-juices) 
diffused  through  the  walls  of  the  blood-capillaries  that  are  not  used  in  the 

nutrition  of  the  tissues  penetrate  the  closed 
lymph-capillaries  by  endosmosis  ;  according 
to  the  second  view  the  tissue-juices  pass 
directly  from  the  tissue  into  the  patent  orifices 
of  the  lymph-capillaries. 

It  is  a  significant  fact  that  the  lymph- 
vessels  of  the  pleura  and  of  the  peritoneum 
are  in  open  communication  with  their  re- 
spective cavities  through  small  openings,  the 
stomata,  between  the  endothelial  cells,  which 
*n  t^ie  P^eura  are  found  at  the  intercostal 
spaces  and  in  the  peritoneum  on  the  central 
tendon  of  the  diaphragm. 


Valve. 


FIG.  65. — LYMPHATIC  VESSEL  OF 
THE  MESENTERY  OF  RABBIT, 
showing  the  boundaries  of  the 
endothelial  cells.  X  50.  Techn. 
No.  48. 


THE   LYMPH-GLANDS. 

The  lymph-glands  (lympho-glandulae, 
lymph-nodes)  are  macroscopic  bodies  inter- 
calated in  the  course  of  the  lymph-vessels. 
Usually  they  are  rounded  oval,  or  flat  kidney- 
shaped  structures  and  differ  greatly  in  size.  At  one  side  there  is  often 
a  scar-like  depression,  the  hilus,  at  which  the  efferent  lymph-vessels 
emerge.  The  afferent  lymph-vessels  penetrate  the  gland  at  various 
points.  Their  construction  becomes  intelligible  if  we  proceed  from 
the  following  conception  :  In  certain  localities  three  to  six  lymph- 
vessels  divide  repeatedly,  the  branches  anastomose,  then  reunite  into 
the  same  or  a  less  number  of  usually  narrower  lymph-vessels.  In  this 
way  a  kind  of  rete  mirabile  *  is  formed.  The  dividing  lymph-vessels  are 

*  Retia  mirabilia  were  first  described  in  connection  with  the  blood-vessels.  They  occur 
along  the  course  of  both  arteries  and  veins  ;  the  vessel  suddenly  breaks  up  into  branches  and 
these  into  capillaries,  which  reunite  into  a  single  vessel.  Exquisite  examples  of  such  networks 
occur  as  the  glomeruli  of  the  kidneys. 


THE    LYMPHATIC    SYSTEM.  123 

called  afferent  vessels  (vasa  afferentia),  the  reuniting,  efferent  vessels  (vasa 
cfferentia).  Within  the  meshes  of  this  reticulum  lie  spherical  and  elon- 
gated masses  that  consist  of  adenoid  tissue.  The  spherical  masses,  the 
secondary  nodules  (follicles),  occupy  the  periphery  ;  the  elongated  masses, 
the  medullary  cords,  the  center  of  the  lymph-gland. 

The  lymph-gland  is  enveloped  in  a  capsule  of  fibrous  connective 
tissue,  which  sends  processes  into  the  interior  of  the  organ,  the  trabeculce 
(Fig.  66).  Finer  extensions  from  the  trabeculae,  in  the  form  of  reticular 
connective  tissue,  pierce  the  walls  of  the  lymph-vessels,  penetrate  the 
secondary  nodules  and  the  medullary  cords,  and  form  a  support  for  the 
numerous  leucocytes  present. 

Capsule.        Secondary  nodule  ("  follicle  '').        Blood-vessel. 


Trabecula. 


Hilus.        Medullary  cords. 
FIG.  66. — SECTION  OF  LYMPH-GLAND  OF  RABBIT.    X  28.     (Schaper.)    Techn.  No.  50. 

The  lymph-glands  consequently  consist  of  a  cortical  and  medullary 
substance,  the  relative  proportions  of  which  vary  greatly.  The  cortex 
contains  the  secondary  nodules,  which  continue  centralward  directly  into 
the  medullary  cords  (Fig.  66).  The  secondary  nodules  and  medullary 
cords  are  surrounded  by  the  sinus-like  continuations  of  the  afferent 
lymph-vessels.  The  latter  here  are  greatly  expanded  and  are  termed 
lymph-sinuses  ;  they  are  pierced  by  the  connective-tissue  reticulum.  The 
lymph-vessels  never  penetrate  the  interior  of  the  secondary  nodules. 
The  secondary  nodules  and  medullary  cords  are  composed  of  adenoid 
tissue  ;  that  is,  of  reticular  connective  tissue,  the  meshes  of  which  are 
crowded  with  leucocytes.  In  many  of  the  secondary  nodules  there  is  a 
light,  spherical  area,  the  germinal  center,  in  which  karyokinetic  figures 


124  HISTOLOGY. 

are  always  to  be  found.  Multiplication  of  cells  also  occurs  in  the  medul- 
lary cords,  but  in  a  much  slighter  degree.  The  secondary  nodules  are 
centers  for  the  formation  of  leucocytes,  which  pass  into  the  lymph- 
sinuses  and  thence  into  the  vasa  efferentia. 

The  capsule  consists  of  fibrous  connective  tissue  and  smooth  muscle- 
fibers,  which  in  the  large  lymph-glands  of  some  animals  are  arranged 
in  long  strands.  The  trabeculae  have  the  same  structure  ;  they  pass 
between  the  secondary  nodes  and  medullary  cords,  but  do  not  come  into 
contact  with  them,  being  separated  from  them  by  the  lymph-sinuses. 
The  walls  of  the  lymph-sinuses  are  formed  of  a  simple  layer  of  plate-like 
cells  ;  similar  cells  clothe  the  surface  of  the  secondary  nodules  and 
medullary  cords,  and  are  also  applied  to  the  trabeculae  and  the  connect- 
ive-tissue reticulum. 


Lymph-sinuses. 


Medullary  cords. 


FIG.  67.— FROM  A  SECTION  THROUGH  THE  MEDULLA  OF  A  LYMPHATIC  NODULE  OF  Ox.  X  51.  In  the 
upper  half  the  trabeculae  and  medullary  cords  are  cut  lengthwise,  in  the  lower  halt  crosswise.  Both 
form  an  anastomosing  network.  In  the  lymph-sinuses  the  fine  fibers  of  the  reticular  connective  tissue 
are  seen,  which  still  contains  leucocytes.  Drawn  with  change  of  focus.  Techn.  No.  51. 

The  structure  of  the  lymph-glands  is  difficult  to  recognize,  owing 
to  several  complications.  These  consist  in  :  I,  the  merging  of  neighbor- 
ing secondary  nodules  ;  2,  the  anastomosis  of  the  medullary  cords  in  the 
form  of  a  coarse  network  ;  3,  the  network  formed  by  the  trabeculae  ; 
4,  the  interlacing  of  the  networks  formed  by  the  medullary  cords  and  the 
trabeculae  ;  5,  the  presence  of  leucocytes  in  the  lymph-sinuses,  which 
must  be  removed  by  special  methods.  The  secondary  nodules,  the 
medullary  cords,  and  the  leucocytes  in  the  lymph-sinuses  form  a  soft 
mass,  that  has  been  named  the  pulp  or  parenchyma  of  the  lymph-gland. 

The  majority  of  the  blood-vessels  enter  at  the  hilus,  the  others  at 
various  points  on  the  surface  of  the  gland.  The  latter  are  smaller 
vessels  and  divide  in  the  capsule  and  in  the  large  trabeculae,  in  the  axes 


THE    LYMPHATIC    SYSTEM.  125 

of  which  they  run.  The  large  artery  entering  at  the  hilus  divides  into  a 
number  of  branches,  that  are  surrounded  by  richly -developed  connective 
tissue.  The  branches  are  principally  distributed  to  the  adenoid  tissue, 
only  a  few  entering  the  trabeculae  ;  they  pass  through  the  lymph-sinuses, 
into  the  medullary  cords,  then  into  the  secondary  nodules,  and  in  both 
situations  break  up  into  rich  capillary  networks  which  supply  the  oxygen 
needed  in  the  formation  of  the  leucocytes.  The  veins  emerge  at  the 
hilus. 

The  nerves  are  few  in  number,  the  supply  including  bundles  contain- 
ing medullated  and  nonmedullated  fibers  ;  their  ultimate  distribution  is 
still  undetermined. 

THE  PERIPHERAL  LYMPH-NODULES. 

(NODULI  LYMFHATICI.) 

Adenoid  tissue  is  not  confined  to  the  lymph-glands  ;  it  occurs  in 
many  mucous  membranes,  in  different  degrees  of  development,  some- 
times as  diffuse,  sometimes  as  definitely  circumscribed  infiltrations 
of  leucocytes.  These  formations  are  not  included  in  the  lymphatic 
system.  More  highly-specialized  structures,  nodules  with  germinal 
centers,  closely  resembling  the  secondary  nodules  of  the  lymph-glands, 
are  also  found  in  the  mucous  membranes  ;  these  are  named  peripheral 
lymph-nodes  and  are  included  in  the  lymphatic  system.  In  many 
mucous  membranes  they  occur  isolated,  as  the  solitary  nodules  (solitary 
follicles),  or  grouped,  as  the  agminated  nodules  (Peyer's  patches),  and 
always  lie  in  a  simple  layer  in  the  tunica  propria  close  beneath  the 
epithelium  (see  the  digestive  organs).  The  number  and  distribution  of 
the  peripheral  lymph-nodes  are  subject  to  considerable  fluctuation, 
not  only  in  the  different  species  of  animals,  but  in  different  individuals  ; 
since  their  mass  varies  and  there  are  frequent  transitions  to  cir- 
cumscribed and  to  diffuse  infiltrations,  it  is  probable  that  they  are 
temporary  structures  that  arise  and  disappear  during  life.  They 
are  distinguished  from  the  real  lymph-glands,  above  all  by  their  less 
intimate  relation  to  the  lymph-vessels,  which  do  not  form  an  encircling 
sinus  for  the  follicle.*  But  the  possession  of  a  germinal  center,  a 
brooding-place  for  young  leucocytes,  appears  in  so  far  to  entitle  them  to 
a  place  in  the  lymphatic  system.  The  young  leucocytes  only  in  part 
enter  the  lymph-vessels  ;  many  wander  through  the  epithelium  to  the 
surface  of  the  mucous  membrane. 

*  The  only  exceptions  occur  in  the  rabbit,  in  which  the  sinus  is  present  in  the  Peyer's 
patches,  but  not  in  the  solitary  follicles. 


126 


HISTOLOGY. 


THE  LYMPH. 

The  lymph  is  a  colorless  fluid  in  which  leucocytes  (lymph-corpus- 
cles) and  granules  are  suspended.  The  latter  are  immeasurably  small, 
consist  of  fat,  and  are  principally  found  in  the  lymph-  (or  chyle)  vessels 
(lacteals)  of  the  intestine  ;  frequently  they  are  present  in  enormous  num- 
bers and  then  they  impart  the  white  color  to  the  chyle.  In  other 
lymph-vessels  the  fatty  granules  occur  sparingly. 


Trabeculse. 


THE  SPLEEN. 

The    spleen    is    a    "  blood-vessel    gland "    and    consists  of  a  con- 
nective-tissue    capsule    and     a    soft    red    mass,    composed     of    blood- 
vessels and  adenoid  tissue,  the  spleen- 

Capsule.  .         pUlp- 

The  capsule  is  invested  by  a 
reflection  of  the  peritoneum,  with 
which  it  is  firmly  united,  and  is  com- 
posed of  dense  fibrous  connective 
tissue,  smooth  muscle-fibers,  and  a 
network  of  elastic  fibers.  Numerous 
cylindrical  or  band-like  prolonga- 
tions, the  trabeculce,  extend  into  the 
interior  of  the  organ,  where  they  form 
a  framework  in  the  spaces  of  which 
lies  the  spleen-pulp.  The  trabeculae 
also  contain  smooth  muscle  -  fibers. 
At  the  hilum  of  the  spleen  the  capsule 
furnishes  special  sheaths  for  the  blood- 
vessels— adventitial  sheaths — which 
blend  with  the  externa  and  accompany 
them  for  long  distances.  The  sheaths 
of  the  arteries  are  the  seat  of  numer- 
ous leucocytes,  that  in  the  form  of  a 
continuous  envelope  accompany  the 

vessel  in  its  entire  course  (as  in  the  guinea-pig),  or  that,  as  in  man, 
the  cat,  etc.,  are  confined  to  certain  localities,  where  they  form  spherical 
masses,  from  0.2  to  0.7  mm.  in  size,  the  so-called  spleen-follicles 
{Malpighian  corpuscles),  Between  these  many  intermediate  forms 
exist,  as  in  the  mouse  and  rabbit. 

The   spleen-follicles  are    usually  situated  in  the  forks  of  the  smaller 


Trabeculae. 


Artery. 


FIG.  68.— FROM  A  CROSS-SECTION  OF  HUMAN 
SPLEEN,  showing  well -developed  spleen- 
follicles,  each  pierced  eccentrically  by  an 
artery.  The  right  branch  of  the  artery  has 
a  continuous  sheath  of  adenoid  tissue.  X  10. 
Techn.  No.  53. 


THE    LYMPHATIC    SYSTEM. 


I27 


arteries,  and  in  such  a  manner  that  the  artery  pierces  the  center  or  the 
side  of  the  follicle.  In  their  minute  structure  they  entirely  agree  with 
the  secondary  nodules  of  the  lymph-glands,  and  even  occasionally 


FIG.  69.— ELEMENTS  OF  HUMAN 
SPLEEN.  X  s6o.  i.  Color- 
less blood-cells.  2.  Epithelial 
cells.  3.  Colored  blood-cor- 
puscles. 4.  Cells  containing 
granules ;  the  upper  one  en- 
closing a  blood-corpuscle,  b. 
Tech n.  No.  52. 


FIG.  70.— RKTICULAR  CONNEC- 
TIVE TISSUE  OF  HUMAN 
SPLEEN.  X  560.  Drawn  from 
the  edge  of  a  shaken  prepara- 
tion. Techn.  No.  53  a. 


FIG.  71. — THREE  KARYOMITO- 
TIC  FIGURES  FROM  A  SECTION 
OF  SPLEEN  OF  DOG.  X  560 
The  filaments  are  not  visible 
with  this  magnification. 
Techn.  No.  54. 


contain  germinal  centers.  The  spleen-follicles  are  also  temporary  struct- 
ures ;  continually  some  are  undergoing  .regressive  change  and  new 
ones  are  developing. 

The  spleen-pulp  forms  a  network  of  cords,  which,  similar  to  those 


•;...  Surface  blackened  by  silver 
precipitate. 


....  Nerves  of  the  pulp. 


Spleen-follicle. 


Small  nerve-bundle.— 


FIG.  72.— SECTION  OF  SPLEEN  OF  MOUSE,  MAGNIFIED  85  TIMES,  showing  the.  nerves  supplying  the  wall 
of  an  artery.  The  boundary  between  the  spleen-pulp  and  the  artery,  the  sheath  of  which  is  infiltrated 
in  its  entire  length  with  leucocytes,  is  indicated  by  a  dotted  line.  Techn.  No.  56. 


of  the  lymph- » lands,  occupy  the  interstices  of  the  trabecular  frame- 
work. Occasionally  the  cords  are  connected  with  the  spleen-follicles. 
The  spleen-pulp  is  composed  of  a  delicate  connective-tissue  reticulum 


128  HISTOLOGY. 

and  numerous  cellular  elements.      The  latter  are  in  part  leucocytes,  in 


Venous  capillar- 
ies ("intermedi- 
ate lacunae  "  of 
other  authors). 

Arterial  capillar- 
ies (continuing 
into  the  venous 
capillaries). 


Vein. 


Artery. 


Trabecula. 


Transition  of 
the  venous 
capil  laries 
'nto — 


Spleen- 
follicle. 


Spleen-pulp. 


FIG.  73,  A.— SECTION  TH-ROUGH  AN  INJECTED  SPLEEN  OF  CAT.    Techn.  No.  57. 


part  slightly  larger  nucleated  cells,  also  cells  containing  colored  blood- 
corpuscles  and  free  colored  blood-corpuscles.  A  granular  pigment  is 
present. 


Venous  capillaries.  N 


Arterial 

capillaries. 


Vein. 


Arter  v. 


Trabecula. 


Transition   of  venous 
capillaries  into — 


Vein. 


Spleen-follicle. 


Splenic  pulp. 


Vein. 

Artery.        ^ 
FIG.  73,  B.— SCHEMATIC  DRAWING  OF  SECTION  -  73,  A. 

The  Blood-vessels. — The  arteries  of  the  spleen  give  off  branches  to  the 


THE    LYMPHATIC    SYSTEM. 

trabeculre  and  to  the  pulp-cords  and  supply  the  dense  capillary  network 
of  the  spleen-follicles.  There  are  no  anastomoses  between  the  arteries. 
The  thin -walled  veins  proceed  from  a  wide -meshed  network  of  capillaries 
(venous  spaces,  venous  capillaries)  occupying  the  intervals  between 
the  trabeculae  and  the  pulp-cords  (Fig.  73).  The  medium-sized  and 
larger  veins  run  alongside  the  arteries  and  frequently  lie  in  furrow- 
like  depressions  in  the  trabeculae.  The  precise  mode  of  communication 
between  the  arteries  and  the  veins  is  not  yet  satisfactorily  determined. 
The  arteries  break  up  into  slender  capillaries  which  do  not  anastomose 
with  one  another.*  According  to  one  view,  the  arterial  capillaries  are 
directly  continuous  with  the  "  venous  "  capillaries  and  the  vascular  chan- 
nels of  the  spleen  are  closed  on  all  sides.  Other  authors  hold  that  the 
arterial  capillaries  pass  into  spaces  without  definite  walls,  "  intermediate 
lacunae,"  which  connect  with  veins  with  perforated,  sieve-like  coats,  and 
that  the  latter  establish  the  communication  with  the  veins  with  closed 
walls. 

The  superficial  lymphatics  on  the  surface  of  the  spleen,  numerous 
in  the  lower  mammals,  are  scantily  developed  in  man.  The  deep  lym- 
phatics in  the  interior  of  the  spleen  are  also  few  in  number  ;  the  exact 
relations  of  the  latter  have  not  yet  been  fully  investigated. 

The  nerves,  consisting  of  a  few  medullated  fibers  and  many  naked 
axis-cylinders,  follow  the  course  of  the  trunks  and  branches  of  the 
arteries,  supply  the  muscle-fibers  of  the  latter  and  of  the  trabeculae  (Fig. 
72).  Plexuses  of  nonmedullated  nerve -fibers  occur  in  the  spleen-pulp, 
that  probably  proceed  from  the  branches  of  the  medullated  nerve-fibers 
just  mentioned,  and  are  in  part  sensory  in  their  nature. 


TECHNIC. 

No.  35. —  The  Heart  and  the  Large  Blood-vessels. — Cut  out  a  papil- 
lary muscle  from  a  human  heart,  a  piece  of  the  aorta  2  cm.  long,  a  piece 
I  or  2  cm.  long  of  the  bronchial  artery  with  its  veins  and  the  surround- 
ing connective  tissue,  a  piece  of  the  renal  vein  I  cm.  long,  and  suspend 
them  on  a  thread  in  a  bottle  containing  40  c.c.  of  absolute  alcohol. 
After  twenty-four  or  forty-eight  hours  the  objects  are  ready  to  section. 
Embed  them  in  liver  (the  artery  and  vein  may  be  embedded  together 
and  will  not  be  injured  by  strong  compression),  cut  thin  cross-sections, 
stain  them  in  Hansen's  hematoxylin,  two  to  five  minutes  (p.  36),  and 
mount  in  damar  (Fig.  53,  56,  57,  58).  The  elastic  fibers  do  not 
stain,  but  with  the  high  power  can  be  often  distinctly  recognized. 

*  In  injected  and  macerated  spleens  the  pulp  can  be  washed  out,  and   then  the   slender 
terminal  branches  of  the  arteries  can  be  seen  lying  together  in  a  leash  or  pencil. 
9 


1 30  HISTOLOGY. 

The  arrangement  of  the  elements  of  the  externa  cannot  be  satis- 
factorily appreciated  in  cross-sections,  often  all  appear  to  be  circularly 
disposed  (a  portion  of  them  are  circularly  arranged — for  example,  those 
of  the  innermost  strata  of  the  external  elastic  membrane).  The  exact 
arrangement  can  only  be  seen  in  longitudinal  sections,  which  also  show 
the  muscle-fibers  of  the  adventitia  plainly. 

No.  36. — Elastic  Fibers  of  the  Blood-vessels. — Stain  objects  fixed  in 
absolute  alcohol,  according  to  No.  35,  with  orcein  (No.  n,  p.  40)  and 
preserve  in  damar-varnish  (Fig.  59). 

No.  37. — Small  Blood-vessels  and  Capillaries. — From  the  base  of  a 
human  brain  slowly  strip  off  pieces  of  the  pia  i  to  3  cm.  in  length  (in 
this  way  delicate  blood-vessels  that  penetrate  the  brain  vertically  are 
withdrawn),  shake  them  in  distilled  water  to  free  them  from  adherent 
fragments  of  brain-tissue,  and  place  them  in  50  c.c.  of  Zenker's  fluid 
(p.  31)  for  one  hour  ;  transfer  them  for  from  one  to  three  hours  to  water 
(for  one  hour  to  running  water),  and  harden  them  in  about  40  c.c.  of 
gradually-strengthened  alcohol  (p..  33).  Examine  one  of  these  pieces 
in  a  watch-glass  on  a  black  background  and  it  will  be  seen  that  small 
vessels  are  isolated. 

a.  With   fine  scissors  cut  off  small  twigs  with   their  ramifications, 
stain  them  for  from  two  to  five  minutes  in  Hansen's  hematoxylin  (p.  36) 
and  mount  in  damar  (Fig.  54). 

b.  From  the  larger   twigs   of  the  cerebral  blood-vessels  cut  pieces 
about  5  mm.  long,  slit  them  open   lengthwise,  stain  them  in    Hansen's 
hematoxylin,  and  place   them   on  a  slide  with  the  adventitia  side  down. 
Mount  in  damar.     By  changing  the  focus  the  three  coats  of  the  vessels 
and  their  general  arrangement  can  be  seen. 

Capillaries  may  be  found  on  examining  fresh  brain-tissue.  They 
are  recognized  by  their  parallel  outlines  and  the  oval  nuclei  of  their 
endothelial  cells  ;  they  are  also  found  in  other  preparations,  for  example 
in  Techn.  No.  9. 

No.  38. — Epithelium  (Endotheliutn)  of  the  Blood-vessels. — Decapitate 
a  rabbit,  open  the  abdomen  by  a  crucial  cut  made  with  the  scissors  ; 
insert  a  cork  frame  about  2  cm.  square  under  the  mesentery,  span 
the  membrane  smoothly  and  fasten  it  with  quills  or  hedgehog  spines, 
taking  care  to  touch  it  as  little  as  possible.  Cut  it  off  all  around  the 
frame  and  place  the  stretched  membrane  with  the  frame  in  20  or  30  c.c. 
of  I  per  cent,  silver  solution.  In  about  thirty  seconds  the  solution  be- 
comes turbid  and  milky  ;  remove  the  frame,  carefully  wash  the  membrane 
with  distilled  water,  place  the  whole  in  a  white  capsule  containing  looc.c. 
of  distilled  water  and  expose  it  to  direct  sunlight.  In  a  few  minutes  a 
brown  coloration  appears.  Now  transfer  the  whole  to  50  c.c.  of  70  per 
cent,  alcohol  (the  membrane  must  be  submerged  in  the  alcohol) ;  in  a  half- 
hour  cut  out  small  pieces  5  or  10  mm.  long  and  mount  them  in  damar. 
In  the  absence  of  sunlight,  take  the  preparation  from  the  silver  solution, 
wash  it,  place  it  for  about  twenty  hours  in  about  30  c.c.  of  70  per  cent, 
alcohol,  then  in  alike  quantity  of  90  per  cent,  alcohol,  and  expose  it  to 


THE    LYMPHATIC    SYSTEM.  13! 

sunlight  on  the  first  opportunity.  It  must  not  be  forgotten  that  the 
whole  blood-vessel  and  not  a  section  of  it  is  present,  so  that  in  order  to 
obtain  a  view  such  as  that  in  Fig.  55  the  surface  of  the  vessel  must  be 
in  focus. 

No.  39. — Elastic  Fenestrated  Membranes. — See  Techn.  No.  14. 

No.  40. — Development  of  Capillaries, — Chloroform  a  seven -day-old 
rabbit,  fasten  it  with  pins  on  a  cork-plate,  open  the  abdomen  by  a  crucial 
incision,  quickly  remove  the  spleen,  stomach,  and  attached  greater  omen- 
turn  and  place  these  parts  in  80  c.c.  of  a  saturated  aqueous  solution  of 
picric  acid  (p.  21).  In  this  solution  the  omentum,  otherwise  difficult  to 
separate,  spreads  out  easily.  After  one  hour  cut  it  off,  transfer  it  to 
60  c.c.  of  distilled  water,  and  divide  it  with  the  scissors  into  pieces  about 
i  cm.  square.  Place  such  a  piece  on  a  dry  slide,  remove  the  water  with 
filter-paper,  and  with  needles  spread  it  out  as  smooth  as  possible,  which  is 
the  more  easily  done  the  less  moisture  there  is  present.  Put  one  or  two 
drops  of  Hansen's  hematoxylin  on  the  preparation.  In  from  one  to  five 
minutes  drain  off  the  hematoxylin  and  place  the  slide  with  the  preparation 
in  a  flat  dish  containing  distilled  water  ;  the  membrane  will  soon  float  from 
the  slide,  but  will  remain  smooth,  and  in  five  minutes  should  be  trans- 
ferred with  the  section-lifter  to  a  watch-glass  containing  eosin  (p.  37),  in 
which  it  should  remain  three  minutes.  It  should  then  be  washed  for  one 
minute  in  distilled  water  and  placed  on  a  slide  ;  the  water  should  be 
absorbed  with  filter-paper,  any  wrinkles  smoothed  out  with  needles,  and 
a  cover-glass  with  a  drop  of  dilute  glycerol  suspended  from  its  lower 
surface  applied.  The  preparation  may  be  mounted  in  damar  instead  of 
glycerol  (that  is,  dehydrated  in  95  per  cent,  alcohol,  cleared  in  oil  of  ber- 
gamot,  and  then  mounted  in  damar),  but  the  finer  structural  details  are 
apt  to  be  lost.  The  colored  blood-corpuscles  are  stained  a  bright  red  by 
the  eosin  (Fig.  61). 

In  spreading  the  membrane  on  the  slide,  delicate  young  capillaries 
may  be  easily  torn  from  the  older  capillaries  and  then  simulate  "  isolated 
cells  containing  blood-corpuscles  ;  "  such  artificial  products  have  been 
described  as  "  vasoformative  cells." 

No.  41. — Colored  Blood-corpuscles  of  Man. — Carefully  cleanse  a  slide 
and  a  small  cover-glass  (finally  with  alcohol).  With  a  clean  needle  prick 
the  finger-tip  at  one  side  ;  lightly  touch  the  first  drop  of  blood  that 
exudes  with  the  cover-glass,  and  without  the  addition  of  any  reagent 
immediately  place  it  on  the  slide.  With  the  high  power  many  colored 
corpuscles  adhering  to  one  another  by  their  broad  surfaces,  forming  the 
so-called  rouleaux,  may  be  seen,  as  well  as  isolated  colored  and  colorless 
blood-corpuscles.  The  distortion  of  many  of  the  colored  corpuscles  is 
due  to  evaporation,  in  consequence  of  which  they  are  beset  with  minute 
spines,  are  crenated.  If  a  drop  of  water  be  placed  at  the  edge  of  the 
cover-glass,  the  corpuscles  soon  become  decolorized  and  the  water 
acquires  a  yellowish  tinge  ;  the  corpuscles  then  become  spherical,  have 
the  appearance  of  pale  circles,  and  finally  disappear.  The  student  is 
advised  to  study  the  decolorization  of  a  single  corpuscle.  In  Fig.  62,  6, 


132  HISTOLOGY. 

the  tinged  area  surrounding  the   bleached  corpuscles  is  somewhat  too 
deeply  shaded. 

No.  42. — Permanent  preparations  of  colored  and  colorless  blood- 
corpuscles  are  made  by  Ehrlich's  dry  method.  The  method  accurately 
carried  out,  after  some  practice,  yields  good  results,  but  with  unskilful 
manipulation  many  caricatures  arise  and  mislead  the  inexperienced.  The 
employment  of  this  method  for  purposes  of  investigation  and  discovery 
requires  great  skill  and  great  caution  in  judgment. 

Preliminary  Manipulations. — For  each  preparation  two  thin  cover- 
glasses  are  required  (they  must  not  be  over  o.i  mm.  thick).  Place  them 
for  a  few  minutes  in  dilute  hydrochloric  acid,  then  in  distilled  water,  and 
finally  in  alcohol.  It  is  best  to  take  cover-glasses  that  have  never  been 
used.  Prepare  a  mixture  of  equal  parts  of  absolute  alcohol  and  ether 
(about  5  c.c.  of  each).  Cleanse  the  tip  of  the  finger  first  with  soap  and 
water,  then  with  a  tuft  of  clean  cotton-wool  moistened  in  the  alcohol- 
ether  mixture.  With  a  clean  needle  (not  previously  used  for  anatomic 
purposes)  prick  the  pad  of  the  finger  that  has  been  made  slightly 
hyperemic  by  compression  ;  take  up  a  cover-glass  with  the  forceps  (not 
with  the  fingers),  press  it  lightly  upon  the  blood  that  exudes  and  place  it 
on  the  second  cover-glass,  with  one  edge  projecting  slightly.  The  drop  of 
blood  will  spread  out  in  a  thin  film  between  the  two  glasses,  which  are 
then  slipped  apart  by  means  of  two  forceps.  By  this  manipulation  the 
influence  of  the  insensible  perspiration  on  the  blood-corpuscles  is  pre- 
vented, which  otherwise  would  shrink  or  lose  their  hemoglobin. 

Exposed  to  the  air,  the  blood  on  the  cover-glasses  dries  in  a 
few  minutes  ;  they  are  then  to  be  placed  in  the  alcohol-ether  mixture 
for  fixation.  In  from  one-quarter  to  two  hours  they  should  be  removed, 
again  dried  in  the  air,  when  they  are  ready  for  further  treatment,  which 
may  be  applied  immediately  or  later,  since  the  preparations  thus  "  fixed  " 
may  be  preserved  for  a  long  time. 

a.  Oxyphile  (Eosinophile,  a)  Granules. — Place  the  cover-glass  prepa- 
rations for  twenty -four,  hours  in  about  4  c.c.  of  distilled  water,  to  which 
about  10  drops  of  eosin  solution   have  been  added.      Rinse  one  minute 
in  distilled  water  and   stain  from   one  to   five  minutes  in  a  watch-glass 
with  Hansen's  hematoxylin  (p.  36).     Transfer  to  distilled  water;   remove 
in  five  minutes   and  let   the  preparations  dry  in   air   under  a  bell-glass. 
Mount   in   damar.       The   colored    blood-corpuscles    and    the    oxyphile 
granules  of  the  colorless  corpuscles   are  stained  a  bright  red,  the  nuclei 
are   blue.       The   oxyphile  granules    occur  in  the  leucocytes  of  normal 
blood,  of  lymph,  and  of  the  tissues,  but  are  uncommon  in  normal  blood. 
A  magnification  of  400  diameters  is  sufficient  to  find  them. 

b.  Rasophile  Granules. — Two  groups  are  distinguished,  the  ^-granules 
and  the   ^-granules.     The  -{-granules  (mast-cell  granules),  which  occur 
only  in  the  leucocytes  of  pathologic  blood,  are   stained  according  to  the 
method  given  in  No.  6.   When  the  staining  is  completed,  proceed  as  in  a. 
The  blue-violet  granules  are  coarser  than  the — 

d-gramiles,  which  occur  in  the  round  nucleated  leucocytes  of  normal 
and  other  blood.  Stain  the  cover-glass  preparations  from  five  to  ten 


THE    LYMPHATIC    SYSTEM.  133 

minutes  in  5  c.c.  of  methylene-blue  solution  (p.  25),  wash,  dry,  and 
mount  in  damar.  These  granules  are  minute  and  scarcely  to  be  seen 
with  the  usual  high-power  dry  lenses;  an  immersion  lens  should  be 
used.  In  staining  with  methylene-blue  not  infrequently  the  film  of  blood 
floats  from  the  cover-glass ;  this  may  be  prevented  by  passing  the  dry 
cover-glass  preparation  rapidly  through  a  flame  before  staining. 

c.  Neutrophile  (e-)  Granules. — Dissolve  (i)  I  gm.  of  orange-yellow 
extra  in  50  c.c.  of  distilled  water;  (2)  I  gm.  of  acid  fuchsin  extra  in 
50  c.c.  of  distilled  water ;  (3)  i  gm.  of  crystalline  methyl-green  in 
50  c.c.  of  distilled  water,  and  let  the  three  solutions  settle.  Then  mix 
II  c.c.  of  solution  (i)  with  10  c.c.  of  solution  (2),  and  add  20  c.c.  of 
distilled  water  and  10  c.c.  of  absolute  alcohol ;  to  this  mixture  add  a 
mixture  of  13  c.c.  of  solution  (3),  10  c.c.  of  distilled  water,  and  3  c.c.  of 
absolute  alcohol.  The  whole  is  then  allowed  to  stand  for  one  or  two 
weeks.  In  this  "  triacid  solution"  the  cover-glass  should  be  placed  for 
fifteen  minutes,  then  washed,  dried,  and  mounted  in  damar.  The  neu- 
trophile  granules,  which  are  found  in  leucocytes  with  lobulated  nuclei,  in 
normal  and  other  blood,  are  of  a  violet  color,  and  are  easily  seen  with 
the  usual  dry  high-power  lenses  ;  the  oxyphile  granules  and  the  colored 
blood-corpuscles  are  of  a  yellow-brown  or  chocolate-brown  color,  the 
nuclei  a  bright  blue-green,  though  their  outlines  are  not  so  distinct  as  in 
the  hematoxylin  preparation. 

No.  43. — Blood-platelets. — rMix  about  5  drops  of  an  aqueous  solu- 
tion of  methyl-violet  (p.  25)  with  about  5  c.c.  of  salt  solution  (p.  19). 
Filter  the  mixture  and  place  a  drop  of  it  on  the  tip  of  the  finger;  prick 
the  finger  through  the  drop  ;  the  blood  as  it  exudes  mixes  with  the 
methyl-violet ;  take  up  a  drop  with  the  cover-glass  and  examine  with 
the  high  power.  The  platelets  are  stained  an  intense  blue,  have  a  peculiar 
luster,  are  disc-shaped,  and  should  not  be  confused  with  the  white 
blood-corpuscles  likewise  stained  blue  (Fig.  62,  9).  They  are  numeri- 
cally variable  elements,  occurring  in  large  numbers  in  the  blood  of  one 
individual,  while  in  the  blood  of  another  they  are  only  to  be  found 
singly  here  and  there.  Care  must  be  taken  not  to  confuse  them  with 
foreign  particles,  which  may  occur  even  in  the  filtered  staining  solution. 

No.  44. —  Colored  Blood-corpuscles  of  the  Frog. — Prepare  the  slide 
and  treat  the  blood  like  No.  41. 

No.  45. — For  Legal  Purposes. — Since  it  is  usually  dried  blood  that 
is  to  be  examined,  dissolve  small  particles  of  dried  blood  in  35  per  cent, 
potash  solution  on  a  slide  ;  blood-stained  pieces  of  linen  may  be  teased 
in  a  drop  of  the  same  solution.  Although  the  colored  blood-corpuscles 
of  domestic  mammalian  animals  are  smaller  than  those  of  man,  it  is 
nevertheless  impossible  from  the  size  of  the  blood-cell  to  determine  its 
source.  On  the  other  hand,  it  is  easy  to  distinguish  the  disc-shaped 
corpuscles  of  mammals  from  the  oval  elements  of  other  vertebrates. 

No.  46. — Colorless  Blood-corpuscles  (Leucocytes)  in  Motion. — Pre- 
liminary manipulations :  Carefully  cleanse  a  slide  and  cover-glass  with 


1 34  HISTOLOGY. 

alcohol.  Kill  a  frog,  grasp  it  by  its  hind  legs,  dry  its  back  somewhat 
with  a  cloth,  and  with  fine  scissors  make  an  incision  I  cm.  long  parallel 
to  and  close  beside  the  vertebral  column.  Introduce  a  capillary  pipet 
into  the  wound  (with  the  tip  directed  forward)  and  suck  the  tip  full.  A 
small  drop  is  sufficient ;  blow  it  on  to  the  slide,  cover  it  quickly,  and 
seal  the  edges  with  melted  paraffin  (p.  48).  Such  a  preparation  shows 
colored  and  colorless  blood-cells  ;  at  first  the  nuclei  of  the  former  are 
indistinct.  The  nuclei  of  living  blood-corpuscles  are  in  general  not  to 
be  seen.  For  the  study  of  ameboid  movement,  select  leucocytes  the 
protoplasm  of  which  is  partly  granular  and  that  are  not  spherical.  The 
movements  are  slow  ;  of  this  one  may  convince  one's  self  by  studying  a 
single  leucocyte  and  making  sketches  of  it  at  intervals  of  from  one 
to  two  minutes.  Study  with  the  high  power  (Fig.  4). 

No.  47. — Blood-crystals. — a.  ' Hemin  crystals  are  easily  obtained. 
Cut  a  small  strip,  about  3  mm.  long,  from  a  piece  of  linen  previously 
saturated  with  blood  and  dried  and  place  it  with  a  pinhead-sized  crystal 
of  common  salt  on  a  clean  slide  ;  add  a  large  drop  of  glacial  acetic  acid 
and  with  a  glass-rod  stir,  the  linen  and  salt  for  about  one  minute,  until 
the  acid  acquires  a  brownish  tinge.  Then  heat  the  slide  over  the  flame 
until  the  acetic  acid  is  evaporated.  Remove  the  linen  and  examine  the 
dry  brown  places  on  the  slide  with  the  high  power  (from  240  diameters 
up).  Occasionally  the  brown  crystals  may  be  seen  without  the  cover- 
glass  and  without  a  mounting  medium,  lying  next  to  numerous  frag- 
ments of  white  salt-crystals  (Fig.  64,  l).  To  preserve,  add  a  large  drop 
of  damar  and  apply  a  cover-glass.  The  hemin  crystals  differ  greatly  in 
form  and  size.  In  the  same  slide  well-developed  crystals  lying  singly, 
crosswise  over  one  another,  or  in  stellate  groups  are  seen,  with  whet- 
stone shapes  and  minute  particles  that  scarcely  exhibit  crystallization. 
The  demonstration  of  the  hemin  crystals  is  of  great  importance  in  foren- 
sic cases.  While  it  is  easy  to  obtain  the  crystals  in  large  stains  on  wear- 
ing apparel,  it  is  difficult,  when  the  stains  are  small,  especially  on  rusty 
iron,  to  prove  that  they  are  from  blood.  The  instruments  and  reagents 
employed  in  such  investigations  must  be  absolutely  free  from  contami- 
nation. 

b.  Hematoidin  crystals  are  obtained  by  teasing  old  blood  extravasa- 
tions ;  they  can  be  recognized  macroscopically  by  their  reddish-brown 
color — for  example,  in  the  corpus  luteum,  in  cerebral  hemorrhages. 

c.  Hemoglobin  crystals  are   obtained  by   transferring    5   c.c.    of  the 
blood  of  a  dog  to  a  test-tube,  adding  a  couple  of  drops   of  ether,  and 
shaking  vigorously  until  the  blood  becomes  lake-colored.     Then  spread 
a  drop  on  a  slide  and  let  the  preparation  dry  in  the  cold.     When  crys- 
tallization has  occurred,  add  a  drop  of  glycerol  and  apply  a  cover-glass. 
The  large  crystals  often   exhibit  a  tendency  to  cleave  lengthwise  (Fig. 
64,  4  a). 

No.  48. — Lymph-vessels. — For  the  study  of  the  walls  of  the  larger 
lymph-vessels  select  the  vessels  opening  into  the  inguinal  glands,  that 


THE    LYMPHATIC    SYSTEM.  135 

arc  large  enough  to  be  taken  out  with  forceps  and  scalpel.      Prepare  like 
the  large  blood-vessels,  No.  35,  or  after  No.  37  b, 

No.  49. — For  the  representation  of  the  more  delicate  lymph-vessels, 
of  their  course  and  arrangement,  the  method  of  interstitial  injection  is 
often  employed.  The  needle  of  a  hypodermic  syringe  filled  with  Berlin- 
blue  is  thrust  haphazard  into  the  tissue  ;  this  is  a  crude  method,  the  results 
of  which  are  of  very  doubtful  value.  Even  though  here  and  there  actual 
lymph-vessels  may  thus  be  filled,  in  most  cases  the  injection-mass  is 
simply  driven  forcibly  into  the  interfascicular  clefts  of  the  connective  tissue. 
The  value  of  any  decision  with  regard  to  "  radicles  of  lymph-vessels  " 
and  to  "  lymph-spaces  "  thus  exhibited  may  be  inferred. 

No.  50. — Lymph-glands. — For  a  general  view  the  mesenteric  glands 
of  kittens  and  young  rabbits  are  suitable.  For  fixation  and  hardening 
place  them  in  30  c.c.  of  absolute  alcohol ;  in  three  days  thin  sections  can 
be  readily  made  and  should  be  taken  so  that  they  pass  through  the 
hilus,  which  is  easily  recognized  macroscopically  by  an  external  depres- 
sion. Longitudinal  sections  passing  through  the  poles  of  the  gland  are 
best,  though  transverse  sections  are  also  useful.  Stain  six  or  eight  sec- 
tions in  Hansen's  hematoxylin  for  from  two  to  three  minutes,  then  in 
eosin.at  the  most  one  minute  (p.  37,  3  b\  transfer  them  to  a  test-tube  half 
filled  with  distilled  water  and  shake  them  for  from  three  to  five  minutes. 
Pour  the  shaken  sections  into  a  flat  dish  ;  the  cortex  and  medulla  can  be 
macroscopically  distinguished  by  the  uniformly  blue  color  of  the  former 
and  the  variegated  appearance  of  the  latter.  Mount  in  damar.  With 
the  lower  power,  fields  similar  to  that  of  Fig.  66  may  be  seen  in  favorable 
sections.  The  trabeculae  are  but  slightly  developed.  The  adipose  tissue 
adhering  to  the  glands  must  not  be  taken  for  reticular  tissue.  High 
magnification  is  of  no  advantage  ;  the  sharp  outlines  disappear  and  the 
picture  loses  in  distinctness. 

No.  5  i . — Lyrnpli-glands  of  mature  animals  and  of  man  are  difficult 
to  understand,  because  the  entire  cortex  is  transformed  into  a  continuous 
mass  sprinkled  with  irregular  germinal  centers.  In  shaking  the  sections 
the  germinal  centers  are  apt  to  fall  out  and  leave  .round  spaces  macro- 
scopically recognizable.  The  lymph-sinuses  can  be  only  indistinctly 
made  out.  The  mesenteric  follicles  of  the  ox  are  well  adapted  for  the 
representation  of  the  network  of  the  medidlary  cords  and  trabccitlce. 
Place  pieces  2  cm.  long  in  200  c.c.  of  concentrated  aqueous  picric-acid 
solution,  and  after  twenty-four  hours,  with  a  sharp  knife  moistened  with 
water,  endeaver  to  cut  thin  sections.  This  is  not  so  easily  done  as  after 
alcohol  fixation,  but  slightly  thicker  sections  can  be  used.  Place  the 
sections  for  one  hour  in  100  c.c.  of  distilled  water,  which  must  be  changed 
frequently,  then  stain  with  Hansen's  hematoxylin  and  eosin  and  shake 
them  (see  No.  50).  Mount  in  damar  (p.  45).  The  trabeculse  are  red, 
the  medullary  cords  blue  ;  with  low  magnification  the  appearance  of  the 
section  is  like  Fig.  67  ;  with  high  magnification  the  reticular  connective 
tissue  of  the  lymph-sinuses  can  be  seen  ;  the  majority  of  the  leucocytes 


136  HISTOLOGY. 

occupying  the  meshes  become  loosened  by  the  treatment  with  picric  acid 
and  are  lost  in  the  shaking. 

No.  52. — Elements  of  the  Spleen. — Make  an  incision  through  a 
fresh  spleen  ;  with  a  scalpel  obliquely  applied  scrape  the  cut  surface  and 
examine  a  little  of  the  red  mass  adhering  to  the  blade  in  a  drop  of  salt 
solution.  Use  the  high  power.  Often,  especially  in  animals,  only 
colored  and  colorless  blood-corpuscles  are  found  ;  some  of  the  latter  con- 
tain minute  granules.  In  human  spleens,  in  addition  to  the  numerous 
colored  blood-corpuscles  altered  in  form,  endothelial  cells  of  the  blood- 
vessels are  found  ;  the  latter  were  formerly  called  "  spleen-fibers  "  (Fig. 
69,  2,  3).  In  many  human  spleens,  multinucleated  cells  containing  blood- 
corpuscles  are  often  sought  in  vain  (Fig.  69,  4). 

No.  53. — The  Spleen. — Without  cutting  it,  "fix"  the  entire  spleen 
in  Muller's  fluid,  using  one  liter  for  a  human,  200  to  300  c.c.  for  a  cat's 
spleen.  After  two  weeks  for  the  cat's,  five  weeks  for  the  human  spleen, 
wash  for  from  one  to  two  hours  in,  if  possible,  running  water,  cut  out 
pieces  2  cm.  square  and  harden  them  in  60  c.c.  of  gradually -strengthened 
alcohol  (p.  33).  Sections  not  too  thin  are  to  be  stained  in  Hansen's 
hematoxylin  and  mounted  in  damar.  If  it  is  desired  to  stain  the  trabec- 
ulae,  after  the  staining  in  hematoxylin  is  completed  place  the  section  for 
one-half  minute  in  eosin.  In  successful  preparations  the  pulp  and  the 
Malpighian  bodies  are  blue,  the  trabeculae  rosy,  the  vessels,  distended 
with  blood-corpuscles,  brown.  If  the  staining  in  eosin  is  prolonged 
beyond  thirty  seconds  the  blood-corpuscles  become  brick-red,  the  tra- 
beculae dark  red,  and  the  distinction  between  them  is  apt  to  be  lost.  The 
sections  are  most  satisfactory  when  examined  with  a  very  low  power 
(Fig.  68)  ;  with  the  high  power  the  outlines  are  often  indistinct.  Fixa- 
tion in  Zenker's  fluid  is  also  recommended. 

No.  53  a. — Reticular  Connective  Tissue  of  the  Spleen. — Shake  a  thin 
section  fixed  and  stained  like  No.  53  for  about  five  minutes  in  a  test-tube 
half  filled  with  distilled  water.  Mount  in  glycerol.  The  leucocytes  are 
difficult  to  dislodge  ;  the  narrow-meshed  network  can  only  be  seen  at  the 
edges  of  the  preparation  (Fig.  70). 

No.  54. — Karyomitotic  Figures  in  the  Spleen  and  Lymph-glands. — 
For  this  purpose  small  pieces  (5  or  10  mm.  long)  of  warm  living  spleen 
and  lymph-glands  should  be  fixed  in  chromic-acetic-osmic  acid  (p.  22), 
and  hardened  in  alcohol.  Stain  thin  sections  in  safranin  (p.  25).  Mount  in 
damar.  The  karyomitotic  figures  of  mammals  are  so  small,  that  with 
the  usual  magnification  (560  diameters),  they  can  only  be  found  by  the 
practised  microscopist.  They  are  detected  by  their  deep-red  color 
(Fig.  71). 

No.  55. — Blood-vessels  of  the  spleen  are  incidentally  obtained  by 
injecting  the  stomach  and  intestine  (compare  with  No.  1 10). 

No.  56. — Nerves  of  Spleen. — For  this  purpose  the  spleen  of  the 
mouse  is  best  suited.  Halve  it  and  apply  Golgi's  method  for  the  demon- 


THE    BONES.  137 


stration  of  the  elements  of  the  nervous  system  (p.  41).  It  is  sometimes 
sufficient  to  place  the  object  in  the  osmio-bichromate  mixture  (in  a  warm 
chamber)  for  three  days  and  for  the  same  length  of  time  in  the  silver 
solution  ;  often  a  repetition  of  the  whole  process  once  or  twice  yields 
good  results. 


III.  THE  ORGANS  OF  THE  SKELETAL  SYSTEM. 

The  skeletal  system  mainly  consists  of  a  large  number  of  hard 
bodies,  the  bones,  which  are  joined  together  by  special  structures  and 
form  in  their  entirety  the  skeleton. 

In  the  embryo  the  greater  part  of  the  skeleton  consists  of  cartilage, 
which  in  the  course  of  development  is  supplanted  by  bone  and  with  the 
exception  of  a  few  remnants  disappears  ;  such  remnants  are  the  costal 
cartilages  and  the  cartilages  of  the  joints,  which  cover  the  articular  sur- 
faces of  many  bones.  Skeletal  cartilages  are  also  found  in  the  respiratory 
passages  and  in  the  organs  of  special  sense. 

THE  BONES. 

On  sawing  through  a  fresh  bone,  at  once  it  will  be  seen  that  its 
texture  is  not  everywhere  alike,  but  that  the  osseous  tissue  appears  in 
two  forms;  the  one,  a  very  dense,  firm,  apparently  structureless  substance, 
constitutes  the  principal  portion  of  the  periphery  and  is  termed  compact 
bone  (substantia  compacts)  ;  the  other,  toward  the  axial  cavity,  appears 
as  an  irregular  reticulum  of  thin  osseous  lamellae  and  slender  trabeculae, 
and  is  called  spongy  bone  (substantia  spongiosa).  The  interstices  of  the 
spongy  bone,  as  well  as  the  central  marrow -cavity,  are  filled  by  a  soft 
mass,  the  bone-marrow  ;  the  surface  of  the  bone  is  enveloped  in  a  fibrous 
membrane,  the  periosteum.  The  proportion  between  the  compact  and 
the  spongy  substance  is  different  in  the  short  bones,  which  consist 
chiefly  of  the  latter,  the  compact  substance  being  limited  to  a  narrow 
zone  at  the  periphery.  Flat  bones  have  sometimes  thicker,  sometimes 
thinner  outer  shells  or  crusts  of  compact  substance,  while  the  interior  is 
filled  with  spongy  substance.  In  the  epiphyses  of  the  long  bones,  as  in 
the  short  bones,  the  spongy  substance  preponderates. 

The  spongy  substance  consists  entirely  of  osseous  tissue  ;  the  com- 
pact substance,  on  the  other  hand,  contains  besides  the  bone  canaliculi 
and  lacunae,  a  second  system  of  coarser  channels,  from  22  to  1 10  ft  wide, 


130  HISTOLOGY. 

which  divide  dichotomously  and  form  a  wide-meshed  network.  These 
channels  contain  the  blood-vessels  and  are  named  haversian  canals.  In 
the  long  bones,  in  the  ribs,  in  the  clavicle,  and  in  the  inferior  maxilla  their 
course  is  parallel  to  the  long  axis  of  the  bone  ;  in  short  bones  they  run 
mainly  in  one  direction,  for  example,  vertically  in  the  vertebrae  ;  in  the 
flat  bones  their  course  is  parallel  to  the  surface,  not  infrequently  along 
lines  that  radiate  from  a  point,  as  in  the  tuberosity  of  the  parietal  bone. 
The  haversian  canals  open  on  the  outer  surface  of  the  bone  (Fig.  74,  x), 
as  well  as  on  the  inner  surface  (Fig.  74,  xx),  directed  toward  the  sub- 
stantia  spongiosa. 


Haversian  canals. 


—     Matrix. 


Periosteum. 


Fat-drops. 


FIG.  74. — FROM  A  LONGITUDINAL  SECTION  OF  A  HUMAN  METACARPUS.  X  30.  Fat-drops  are  seen 
in  the  Haversian  canals.  At  x  Haversian  canals  open  on  the  outer,  and  at  xx  on  the  inner  surface 
of  the  bone.  Techn.  No.  58. 


The  ground-substance  of  compact  bone  is  arranged  in  lamellae,  that 
is,  the  osseous  fibrillae  are  joined  in  bundles,  and  these  placed  side  by 
side  form  thin  plates  or  lamellae.  According  to  .the  disposition  of  these 
plates  three  lamellar  systems  may  be  distinguished  :  an  annular  or 
haversian  system,  which  in  cross-sections  exhibit  eight  to  fifteen  lamellae 
concentrically  arranged  around  an  haversian  canal  ;  these  lamellae  are 
called  haversian  or  special  lamella  (Fig.  75).  Between  the  haversian 
lamellar  systems,  that  come  into  contact  only  here  and  there,  are  irregu- 
larly-disposed lamellae,  the  interstitial  lamella  ;  these  are  connected  with 
the  third  lamellar  system,  the  circumferential  lamella,  in  which  the  osse- 


THE    BONES.  139 

ous  strata  encircle  the  outer  and  occasionally  the  inner  free  surface  of  the 
bone.  The  circumferential  lamellae  contain  an  extremely  variable  number 
of  channels  for  blood-vessels,  which,  unlike  the  haversian  canals,  are  not 
the  centers  of  annular  systems  of  lamellae  ;  they  are  called  Volkmann's 
canals  and  the  contained  vessels,  the  "  perforating  vessels."  The  latter 
frequently  connect  with  the  vessels  of  the  haversian  canals  ;  the  passage 
of  the  Volkmann's  canals  into  the  latter  is  a  very  gradual  one.  The 
bone  lacunae  in  the  compact  substance  have  a  definite  position.  In  the 
haversian  systems  their  long  axis  is  parallel  to  the  long  axis  of  the 


„    Periosteum. 

Outer  circumferential 

lamellae. 
•y   Haversian  canals. 


Haversian  lamellae. 


Interstitial  lamellae. 


Inner  circumferential 
lamellae. 


/  Marrow. 


FIG.  75.— FROM  A  CROSS-SECTION  OF  A  METACARPUS  OF  MAN.     X  50.     The  haversian  canals,  h,  still 
contain  marrow  (fat-cells).    Techn.  No.  58. 

haversian  canals  and  they  are  bent  so  that  cut  transversely  in  the 
cross-section  of  an  haversian  canal  they  appear  concentrically  curved. 
In  the  interstitial  lamellae  the  lacunae  are  placed  irregularly  ;  in  the 
circumferential  lamellae  so  that  their  surfaces  extend  parallel  to  the  sur- 
faces of  the  lamellae.  The  bone  canaliculi  open  into  the  haversian  canals 
and  on  the  free  outer  and  inner  surfaces  of  the  bone. 

The  bone-marrow  occupies  the  axial  cavity  of  the  tubular  bones,  fills 
the  interstices  of  the  spongy  substance,  and  is  also  found  in  the  larger 
haversian  canals.  It  is  of  a  red  or  yellow  color  and  therefore  two 
varieties  are  distinguished,  the  red  marrow  and  the  yelloiv  marrow.  The 
red  marrow  is  found  in  the  flat  bones,  in  the  vertebrae,  in  the  base  of  the 
skull,  in  the  sternum,  in  the  ribs,  and  in  all  young  bones  (also  in  all  the 
long  bones  of  small  animals)  ;  the  yellow  marrow  occurs  in  the  short  and 
long  bones  of  the  extremities.  In  old  and  in  sick  persons  the  marrow  is 
mucoid  and  reddish-yellow  and  is  then  called  gelatinous  bone-marrow  ;  it 
is  only  characterized  by  its  poverty  in  fat. 

The  elements  of  red  marrow  comprise  a  delicate  connective-tissue 


I4O  HISTOLOGY. 

reticulum,  a  few  fat-cells,  larger  and  smaller  marrow-cells,*  and  giant-cells 
(myeloplaxes)  (Fig.  76).  In  the  larger  marrow-cavities  the  connective 
tissue  forms  a  membrane,  the  endosteum,  which  lines  the  free  surface. 
The  marrow-cells  exhibit  manifold  forms  resembling  leucocytes  ;  the 
giant-cells  are  structural  anomalies  representing  leucocytes  enlarged  and 
altered  in  form  ;  they  are  huge,  extremely  irregular,  uninucleated,  or 
multinucleated  masses  of  protoplasm.  The  shape  of  the  nucleus  varies 

Eosinophilous-cell  (granule-cell). 

Marrow-cell  (plasma-cell). 


Giant- 
cell. 


Marrow- 
-,  ---   cell(plasma- 


Connective-tissue  reticulum. 


Fat  space. 


Eosinophilous-cell  (granule-cell). 


FIG.  76.— SECTION  OF  BONE-MARROW  OF  RABBIT,  SHOWING  THE  DELICATE  CONNECTIVE-TISSUE 
RETICULUM  CONTAINING  THE  DIFFERENT  ELEMENTS  OF  THE  MARROW.     X  400.     (Schaper). 

greatly  ;  it  may  be  round,  lobulated,  band-  or  hoop-shaped,  or  it  may 
fashion  a  network.  A  uninuclear  giant-cell  may  become  multinuclear 
through  the  division  of  the  nucleus  by  constriction,  or  a  corresponding 
part  of  the  protoplasm  may  be  set  free  with  the  nucleus  and  the  result  is 

*  The  attempt  has  been  made  to  classify  the  cells  of  bone-marrow  according  to  their  source, 
cells  with  a  slightly-developed  cell-body  (Fig.  77,  l)  having  been  named  "lymphocytes,"  those 
with  a  well-developed  cell-body  (3,4,  5)  "myelocytes."  The  possibility  that  the  lymphocytes 
originate  not  only  in  the  lymph-glands  and  related  organs,  but  also  in  the  bone-marrow,  can  not 
be  excluded  ;  likewise,  the  occurrence  of  myelocytes  in  the  spleen  and  occasionally  in  the 
lymph-glands  is  certain.  Further,  if  the  fact  that  numerous  intermediate  forms  exist  is  consid- 
ered, the  untenableness  of  this  attempted  classification  is  evident. 


THE    BONES.  14! 

a  uninuclear  cell.  The  supposition  that  these  processes  of  division  indi- 
cate the  phenomena  of  a  reversed  series  of  processes,  the  merging  of 
several  cells  into  one,  has  very  little  probability,  since  the  process  of 
budding  has  been  observed  in  living  cells.  Finally  there  are  found  in 
the  red  marrow  nucleated  cells  with  yellow-colored  protoplasm  like  that 


-----  7  Hematoblasts. 

£-''' 

—      Colored  blood-corpuscle. 


:0-^ 

^MJBT- Giant-cell. 


FIG.  77.  —  ELEMENTS  OF  HUMAN  BONE-MARROW.     X  600.     1-5.   Various  forms  of  bone-cells. 
6.  Eosinophilous  cell.     Techn.  No.  59  b. 

of  the  colored  blood-corpuscles  ;  these  are  the  mother-cells  of  the  colored 
blood-corpuscles,  the  hematoblasts  (erythroblasts)  (Fig.  76  and  Fig.  77). 
Yellowish  pigment-granules  that  appear  in  the  different  cells  are  regarded 
as  the  remains  of  disintegrated  colored  blood-corpuscles. 

The  yellow  marrow  consists   of  a  connective  -tissue  reticulum  con- 


~  .    "  -^  -  "= — ^-^ Outer  fundamental 

_^_jL^-*      .       L;-  ::^  '       .    ~     -  lamellae. 

Volkmann  s  canals.   — =rm2        ~  -     XV  »  *   ~     ^          ~ 

"^ = = 1'  «^v  ,   .     "  ^ 

~~               "        ^*     "•      f   f    " 
_       ^        —":  \,~\     y-    ' ''„"      t    a  £j    '  — * — = = •  Haversian  lamellae. 

Sharpey 's  fibers.  ^~f/~~^L^\  1  ^    -  "  <  ^   >  -J  *^P^  \*  Haversian  canal. 

Interstitial  lamellae. 


FIG.  78.— FROM  A  CROSS-SECTION  OF  THE  FEMUR  OF  ADULT  MAN.    X  80.    Techn.  No.  57.    The  lamellae 
can  be  recognized  by  the  disposition  of  the  lacunae. 

taining  much  fat.      Marrow-cells  and  hematoblasts  in  yellow  marrow  are 
found  only  in  the  head  of  the  humerus  and  the  femur. 

The  periosteum  is  a  compact  connective-tissue  membrane,  in  which 
two  layers  can  be  distinguished.  The  outer  layer  is  characterized  by  its 
richness  in  blood-vessels  and  forms  the  connection  with  adjacent  struct- 
ures, tendons,  fasciae,  etc.;  the  inner  layer  contains  few  blood-vessels, 


142  HISTOLOGY. 

but  is  very  rich  in  elastic  fibers  running  parallel  with  the  long  axis  of  the 
bone  and  spherical  or  spindle-shaped  connective -tissue  cells.  Here  and 
there  on  the  inner  surface  a  layer  of  cubical  elements  may  be  found, 
that  are  of  importance  in  the  development  of  the  bone.  The  periosteum 
is  sometimes  firmly,  sometimes  loosely  attached  to  the  bone  ;  the  attach- 
ment is  secured  by  the  blood-vessels  passing  to  and  from  the  bone  and 
by  Sharpey's  fibers,  which  pierce  the  circumferential  and  adjacent  inter- 
stitial lamellae  and  extend  in  all  directions  (Fig.  78).  In  the  tubular 
bones  elastic  elements  of  the  inner  layer  of  the  periosteum  penetrate  the 
bone  in  company  with  Sharpey's  fibers  and  without  regard  to  the  lamellar 
structure,  run  in  the  more  superficial  strata.  Elastic  fibers  also  occur 
that  penetrate  independently  of  Sharpey's  fibers.  In  the  bones  of  the 
vertex  of  the  skull  elastic  elements  are  wanting. 

The  blood-vessels  of  the  bone,  the  marrow,  and  the  periosteum  are 
in  the  closest  connection  with  one  another,  and  also  with  surrounding 
structures.  Small  branches  (not  capillaries)  of  the  numerous  arteries 
and  veins  of  the  periosteum  enter  the  haversian  and  Volkmann's  canals, 
which  on  the  inner  surface  of  the  bone  are  in  communication  with  the 
blood-vessels  of  the  marrow.  The  latter  is  supplied  by  the  nutrient 
artery,  which  on  its  way  through  the  compact  substance  gives  off 
branches  to  the  same,  and  in  the  marrow  breaks  up  into  a  rich  vascular 
network.  The  veins  that  take  up  the  capillaries  of  the  marrow  have  no 
valves.  Lymph-vessels  with  well-defined  walls  occur  only  in  the  most 
superficial  layers  of  the  periosteum. 

The  nerves  are  numerous  and  consist  partly  of  medullated,  partly  of 
gray  fibers.  They  enter  the  haversian  canals,  the  bone-marrow,  and 
the  periosteum,  and  in  the  latter  occasionally  terminate  in  Pacinian 
corpuscles. 

THE  ARTICULATIONS  OF  BONES. 

Two  forms  of  articulations  are  recognized  :  I,  synarthroses,  joints 
characterized  by  immobility  ;  2,  diarth roses,  joints  in  which  the  bones 
are  movable,  one  upon  the  other. 

In  synarthroses  the  bones  are  joined  either  by  ligaments,  the  union 
constituting  a  syndesmosis  ;  or  by  the  intervention  of  cartilage,  forming  a 
synchondrosis. 

The  ligaments  are  partly  fibrous  bauds,  possessing  a  structure  like 
that  of  tendon,  partly  elastic  bands.  The  latter  are  distinguished  by  the 
possession  of  numerous  robust  elastic  fibers,  which  are  never  arranged 
in  bundles  or  lamellae,  but  are  always  separated  by  loose  connective 
tissue.  The  ligamentum  nuchae,  ligamenta  subflava,  and  ligamentum 
stylohyoideum  are  elastic  ligaments  (Fig.  23,  C). 


THE    BONES. 


143 


The  sutures  also  belong  to  the  syndesmoses  ;  they  are  short  fibrous 
ligaments  that  extend  from  one  serrated  osseous  edge  to  the  other. 

The  cartilage  in  synchondroses  is  rarely  only  of  the  hyaline  variety, 
but  usually  is  in  part  fibro-cartilage  (especially  at  the  borders  in  contact 
with  the  bone)  and  in  part  hyaline,  in  which  the  cell-capsules  are  fre- 
quently calcified. 

The  intervertebral  ligaments,  which  belong  to  the  synchondroses, 
possess  in  their  center  a  soft,  gelatinous  substance,  the  nucleus  pul- 
posus,  that  contains  large  groups  of  cartilage  cells  ;  it  is  the  remains 


Hyaline  cartilage. 


Striated  zone. 
Calcified  cartilage. 

Bone. 

Marrow  (fat-cells). 

Blood-vessel. 

FIG.  79. — VERTICAL  SECTION  THROUGH  THE  HEAD  OF  A  METACARPUS  OF  ADULT  MAN.    X  50. 

Techn.  No.  60. 

of  the  notochord,  the  embryonic  precursor  of  the  vertebral  column. 
At  the  periphery  of  the  intervertebral  ligaments  there  is  a  narrow  ten- 
dinous zone. 

In  diarthroses  the  parts  entering  into  a  joint  are  the  articular  ends 
of  the  bones,  the  capsular  ligament,  the  marginal  fibro-cartilages  (labra 
glenoidalia),  and  the  interarticular  cartilages  (menisci). 

The  articular  ends  of  the  bones  are  covered  by  a  stratum  of  cartil- 
age from  0.2  to  5  mm.  thick  thinning  toward  the  edges.  The  superficial 
cartilage  cells  are  flattened  and  placed  parallel  to  the  surface ;  those  in 


144 


HISTOLOGY. 


the  median  strata  are  rounded  *  and  are  often  collected  in  groups  ;  in 
the  deepest  strata  the  groups  of  cells  are  partly  arranged  in  longitudinal 
rows,  vertical  to  the  surface  of  the  bone  ;  attached,  but  separated  by  a 
narrow  striated  belt,  is  a  small  zone  of  calcified  cartilage  interposed  be- 
tween and  connecting  the  hyaline  cartilage  and  the  osseous  tissue  (Fig. 
79).  Not  all  the  articular  cartilages  exhibit  the  structure  just  described  ; 
the  cartilages  of  the  costo-vertebral,  the  sterno-clavicular,  the  acromio- 
clavicular,  and  the  maxillary  articulations,  and  the  head  of  the  ulna  are 
not  hyaline,  but  fibro-cartilage  ;  the  distal  articular  surface  of  the  radius 
is  covered  with  dense  fibrous  tissue. 

The  glenoid  ligaments  and  the  interarticular  cartilages  do  not  exhibit 
the  characteristic  cartilage  matrix  ;  they  consist  of  a  compact  fibrous  con- 
nective tissue  and  of  spherical  cells.     To  the 
same  category  belong  the  so-called   sesamoid 
cartilages.       The     tendinous    sheath    of    the 
cuboid,  however,  contains  genuine  cartilage. 
In    the  adult,  nerves   and   blood-vessels 
are  wanting  in  the  articular  cartilages,  also  in 
the    interarticular   cartilages  and  the  glenoid 
ligaments. 

The  capsular  ligaments  consist  of  an  ex- 
ternal fibrous  layer  (stratum  fibroswri)  varying 
greatly  in  thickness,  possessing  a  structure 
like  that  of  the  ligaments  above  described, 
and  of  an  internal  membrane,  the  stratum 
synoviale,  the  free  inner  surface  of  which  is 
smooth  and  glossy  ;  the  outer  layer  of  the 
latter  is  composed  of  loose  elastic  fibers  and 
fibrillar  connective  tissue  here  and  there  con- 
taining fat-cells  ;  within  this  is  a  thin  lamella 
of  parallel  connective-tissue  bundles,  in  which, 
toward  the  interior,  there  are  small  spherical 

or  stellate  cells,  1 1  to  17^  in  size,  containing  a  large  nucleus  ;  the  latter  are 
sometimes  few  in  number — at  points  subjected  to  more  pressure — some- 
times very  abundant,  and  form  an  endothelial  membrane  three  or  four 
strata  thick. 

The  synovial  membrane  (stratum  synoviale)  often  forms  folds  contain- 
ing fat  that  project  into  the  synovial  cavity  and  bears  on  its  free  surface 


FIG.  80. — SYNOVIAL  VILLI  WITH 
BLOOD-VESSELS  FROM  A  HUMAN 
KNEE-JOINT.  X  50.  The  epi- 
thelium has  fallen  from  the  apex 
of  the  left  villus,  exposing  the 
connective  tissue.  Techn.  No. 
61. 


*  Recently,  the  cells  of  the  articular  cartilages  have  been  described  as  having  processes 
which  extend  into  the  adjacent  cartilaginous  matrix.  The  cells  of  the  deeper  strata  are  said  to 
possess  lobulated  nuclei. 


THE    BONES.  145 

the  synovial  fringes  or  villi ,  variously-shaped  processes,  mostly  of 
microscopic  size,  which  are  particularly  closely  set  on  the  edges  of  the 
joint -surfaces  and  bestow  upon  the  synovial  membrane  a  reddish,  velvety 
appearance.  They  consist  of  connective  tissue  and  are  clothed  by  a 
single  or  double  layer  of  endothelial  cells. 

The  larger  blood-vessels  of  the  synovial  membrane  lie  in  the  loose 
connective-tissue  layer ;  from  here  the  capillaries  extend  through  the 
inner  thin  connective -tissue  stratum  and  penetrate  the  villi.  Some  of 
the  villi  are  nonvascular.  The  lymph-vessels  lie  close  under  the 
endothelium. 

The  nerves  run  in  the  loose  connective  tissue  and  in  part  terminate 
in  Pacinian  corpuscles. 

The  synovia  contains  more  or  less  profoundly  altered  cells,  fragments 
of  cells,  and  oil-globules,  all  the  product  of  physiologic  processes  of 
waste  of  the  surfaces  of  the  synovial  membrane  and  articular  cartilage  ; 
also  albumin,  mucus,  and  salts  ;  the  solids  amount  to  six  per  cent.,  the 
remainder  consists  of  water. 

THE  CARTILAGES. 

The  costal  cartilages  are  of  the  hyaline  variety  ;  the  matrix  exhibits 
the  peculiarities  previously  mentioned  (p.  83),  the  cells  frequently  con- 
tain fat.  The  surface  is  enveloped  by  a  compact  fibrous  membrane,  the 
perichondrium,  which  consists  of  interlacing  fibrous  bundles  and  elastic 
fibers. 

The  articular  cartilages  are  covered  by  the  perichondrium  only  at 
their  edges,  not  on  their  free  surface.  Where  the  cartilage  and  the 
perichondrium  are  in  contact  there  is  a  gradual  transition  of  the  one 
tissue  into  the  other  and  consequently  the  attachment  between  the  two 
is  very  firm. 

The  perichondrium  carries  the  nerves  and  the  blood-vessels  ;  the 
latter  also  run  in  excavated  canals  within  growing  cartilage.  In  the  adult, 
cartilage  is  devoid  of  blood-vessels  ;  the  nutrition  of  the  tissue  depends 
upon  diffusion  from  the  surface.  The  costal  cartilages  in  advanced  life 
often  contain  blood-vessels  because  of  beginning  ossification. 

The  cartilages  of  the  special-sense  organs  and  of  the  respiratory 
organs  will  be  described  in  the  respective  chapters. 

DEVELOPMENT  OF  BONE. 

The  bones  are  relatively  late  structures  to  appear.  The  develop- 
ment of  the  muscles,  nerves,  blood-vessels,  brain,  spinal  cord,  etc.,  is 


146 


HISTOLOGY. 


already  well  advanced  in  the  embryo  at  a  time  when  not  a  trace  of 
bone  is  present.  At  that  period  the  skeleton  is  formed  of  hyaline 
cartilage.  With  the  exception  of  certain  parts  of  the  cranium  and  nearly 
all  the  bones  of  the  face,  the  entire  skeleton  is  represented  by  cartilage. 
In  the  upper  extremity,  for  example,  the  humerus,  radius,  ulna,  carpus, 
and  the  skeletal  parts  of  the*  hand  consist  of  cartilaginous  pieces,  that 
are  not  hollow  like  the  bones  by  which  they  are  subsequently  replaced, 
but  solid  throughout.  The  osseous  skeleton  then  gradually  appears 
in  the  place  of  the  cartilaginous  skeleton.  All  the  osseous  parts  that 
in  the  embryo  were  preceded  by  cartilage  are  called  primary  or 


Hyaline  cartilage.' 


Center  of  calcification. 


'  '.*;r        Osteogenetic  tissue. 
Perichondral  bone. 

•*•**•-       Calcified  matrix. 


Hyaline  cartilage. 


FIG.  81. — FROM  A  DORSO-PLANTAR  LONGITUDINAL  SECTION  OF  THE  GREAT  TOE  OF  A  FOUR  MONTHS' 
HUMAN  EMBRYO.  Two-thirds  of  the  first  phalanx  represented.  X  5°-  i-  Lacunae  enlarged  and 
containing  many  cartilage-cells.  The  cells  cannot  be  distinguished  with  this  magnification,  only 
their  nuclei,  which  appear  as  minute  dots.  At  2,  developing  cartilage  ;  cells  in  groups  of  three  and 
four,  each  group  produced  by  repeated  division  of  one  cartilage-cell.  Techn.  No.  62. 

endochondral  bone ;  the  other  bones,  not  preformed  in  cartilage,  are 
named  secondary  or  intermembranous  bone. 

The  primary  bones  include  all  the  bones  of  the  trunk  and  extremities, 
the  greater  part  of  the  base  of  the  cranium  (the  occipital  bone  with  the 
exception  of  the  upper  portion  of  the  tabular  part,  the  sphenoid  bone 
with  the  exception  of  the  internal  pterygoid  plate,  the  temporal  bone  with 
the  exception  of  the  squamous  portion,  the  ossicles  of  the  ear,  the  eth- 
moid bone,  the  inferior  turbinal),  and  the  hyoid  bone. 

The  secondary  bone  includes  the  bones  forming  the  sides  and  vertex 
of  the  cranium  and  nearly  all  the  bones  of  the  face. 


THE  BONES.  147 

DEVELOPMENT  OF  PRIMARY  BONE. 

Two  modes  of  bone  formation  are  here  to  be  considered  :  i,  endo- 
chondral formation,  formation  of  osseous  tissue  within  the  cartilage  pres- 
ent, 2,  periostcal  (better  perichondral}  formation,  formation  of  osseous 
tissue  immediately  surrounding,  therefore  upon,  the  cartilage.  The  phylo- 
genetically  older  perichondral  ossification  usually  begins  earlier,  but  for 
didactic  reasons  will  be  described  subsequently  to  the  process  of  endo- 
chondral formation. 

i.  ENDOCHONDRAL  OSSIFICATION. — The  first  indications  of  this  pro- 
cess consist  in  changes  at  certain  places  within  the  cartilage ;  the  cells 


te« 


jjTnffirffi      Enlarged  lacuna. 
Osteogenetic  tissue. 

Endochondral  bone.     -  tM^'  ''^PS:3^fj   —  !  Calcified  cartilage  trabeculae  projecting 

into  the  primary  marrow-space. 

•ri^^feXTKJ-: 
Blood-vessels. 

Perichondral  bone. 

.  ,  .^        ,  Perichondral  bone. 

Enlarged  lacunae. 

i  V  '"'•""" 

FIG.  82.  — FROM  A  DORSO-PALMAR  LONGITUDINAL  SECTION  OF  THE  FINGER  OF  A  FOUR  MONTHS' 
HUMAN  EMBRYO.  Two-thirds  of  the  second  phalanx  represented.  X  50.  The  calcified  trabeculae  are 
covered  by  a  thin  layer  of  endochondral  bone.  (More  highly  magnified  in  Fig.  83.)  Techn.  No.  62. 

enlarge  and  divide,  so  that  several  lie  in  one  lacuna ;  a  deposition  of  lime 
salts  takes  place  within  the  matrix,  in  consequence  of  which  it  becomes 
granular  and  dull,  it  calcifies.  Such  places  may  be  recognized  by  the 
unaided  eye,  and  are  called  centers  of  ossification  (better,  centers  of  calci- 
fication). The  portions  of  the  cartilage  remote  from  the  center  of 
calcification  continue  to  grow  in  thickness  and  length,  while  at  the  center 
growth  ceases,  and  consequently  the  cartilage  at  this  point  appears  con- 
stricted (Fig.  82).  Meanwhile,  on  the  surface  of  the  center  of  calcifica- 
tion a  tissue  rich  in  blood-vessels  and  young  cells,  the  osteogenetic  tissue* 

*  This  is  not  a  good  name,  inasmuch  as  the  tissue  has  not  originated  from  bone,  but  is 
to  become  bone. 


148 


HISTOLOGY. 


has  made  its  appearance.     This  penetrates  into   the  cartilage  and  causes 
the  breaking   down   of  the  calcified  matrix  ;   the  cartilage-cells  are   set 


Hyaline     carti- 
lage (cells  re- 
arranged in 
vertical 
rows). 


Hyaline  car- 
tilage (cells 
enlarged). 


Periosteum 


Osteoblasts. 


Osteoblasts.        Blood- 
vessels. 


Giant-cells. 


Endochondral  bone. 
Marrow- 
cells. 


FIG.  83.— FROM  A  LONGITUDINAL  SECTION  OF  THE  PHALANX  OF  THE  FIRST  FINGER  OF  A  FOUR  MONTHS' 
HUMAN  EMBRYO.  X  220.  In  theendochondral  bone  irregular  lacunae  with  bone-corpuscles  are  seen. 
Techn.  No.  62. 

free  and  disintegrate.       In  this  way  a  little  excavation  has   arisen  in  the 
center  o'f  calcification  ;  it  is  called  the  primary  marro-cv- cavity, 

These  processes  are  repeated  in  the  immediately  surrounding  carti- 


THE    BONES. 


149 


lage  ;  that  is,  the  matrix  calcifies,  the  cartilage-cells  enlarge,  new  portions 
of  the  cartilage  break  down,  and  as  a  result  the  primary  marrow-space  is 
gradually  and  continuously  enlarged.  At  the  same  time  the  capsules  of 
many  cartilage-cells  are  opened,  the  cells  degenerate,  and  the  intervening 
calcified  matrix  projects  into  the  marrow-space  in  the  form  of  irregular 
processes  or  trabeculae.  The  primary  marrow-cavity  now  is  a  little  bay 


Blood-vessel.     Marrow. 


FIG.  84.— CROSS-SECTION  OF  THE  UPPER  HALF  OF  THE  DIAPHYSIS  OF  THE  HUMERUS  OF  A  FOUR 
MONTHS'  HUMAN  EMBRYO,  h.  Developing  haverstan  spaces  ;  h',  blood-vessel.  X  35-  Techn.  No.  62. 

filled  with  blood-vessels  and  young  cells.  The  fate  of  these  cells  in  the 
further  course  of  development  varies  greatly.  They  retain  their  original 
form  and  become  marrow-cells,  or  they  become  fat-cells,  or — and  this  is 
most  important — they  become  bone-forming  cells,  osteoblasts.  In  the 
latter  event,  a  number  of  cells  arrange  themselves  in  a  single  layer  on 
the  walls  of  the  marrow-cavity  and  on  the  surface  of  the  calcified  trabe- 
culae and  produce  the  matrix  of  osseous  tissue. 

As  a  result  of  the  activity  of  the  osteoblasts,  the  trabeculae  and 
the  walls  of  the  marrow-cavity  are  soon  covered  with  a  thin  layer  ol 
bone-substance,  gradually  increasing  in  thickness.  Thus  step  by  step 
the  former  solid  cartilage  is  transformed  into  spongy  bone,  the  trabeculae 
of  which  still  contain  a  residue  of  calcified  cartilage-matrix  (Fig.  84). 


I  50  HISTOLOGY. 

2.  PERICHONDRAL  OSSIFICATION. — This  mode  of  bone  formation  is 
also  accomplished  through  the  agency  of  the  osteoblasts  *  derived  from 
the  osteogenetic  tissue  at  the  surface  of  the  center  of  calcification  (Fig. 
81).  Through  the  activity  of  the  osteoblasts  strata  of  plexiform  osseous 
tissue  are  periodically  formed  on  the  surface  of  the  cartilage  ;  these  osseous 
masses  are  distinguished  from  the  endochondral  bone  by  the  absence  of 
remnants  of  calcified  cartilaginous  matrix,  because  the  perichondral  bone 
is  formed  at  the  circumference  and  not  in  the  interior  of  the  cartilage. 
The  formation  of  the  first  haversian  canals  may  be  observed  in  the  peri- 
chondral bone  (Fig.  84).  The  latter  is  not  formed  in  a  continuous  layer 
of  uniform  thickness,  but  at  frequent  intervals  depressions  or  recesses 
may  be  observed  containing  blood-vessels  surrounded  by  osteoblasts 
(Fig.  84,  h  /i)  ;  at  first  the  recesses  are  open  toward  the  periphery,  but 
with  the  progressive  development  of  the  osseous  strata  they  are  closed  in 
and  then  represent  haversian  canals.  The  osteoblasts  enclosed  within 
the  canals  produce  new  osseous  strata,  the  future  haversian  lamellae. 


'\-'      "1;-— -•'---> -^r—  Bone-cell. 

Cartilage-cell.    — = — L  ^  \  ^        v«  r 

-;. 

SV,  '„ Bone-matrix. 

Cartilage-matrix.  J, ...  '"^-^ 


-   Transitional  form  of  a  cartilage- 
cell  undergoing  conversion  into 
/-  a  bone-cell. 

FIG.  85.— FROM  A  CROSS-SECTION  OF  THE  LOWER  JAW  OF  A  NEWBORN  DOG.    X  240.    Metaplastic  type. 

Techn.  No.  62. 


By  the  absorption  of  the  cartilage  and  by  its  substitution  by  osseous 
tissue,  also  by  the  deposition  of  bone-substance  on  its  exterior,  the  piece 
of  cartilage  has  become  a  bone. 

The  essence  of  the  foregoing  processes  consists  in  an  absorption  of 
the  parts  of  the  primordial  skeleton  and  in  a  reconstruction  of  the  same 
by  the  development  of  bone-substance.  This  mode  of  bone  formation  is 
termed  neoplastic  in  contradistinction  to  the  rarer  metaplastic  mode,  in 
which  the  cartilage  is  not  destroyed  but  is  ossified,  and  the  cartilage- 
matrix  becomes  the  bone-matrix,  the  cartilage-cells  the  bone-cells  (as,  for 
example,  in  the  angle  of  the  inferior  maxilla)  (Fig.  85). 


*  In  the  inner  strata  of  the  perichondral  osseous  cortex  the  osteoblasts  are  almost  entirely 
absent ;  also  in  the  region  of  the  endochondral  osseous  trabeculae  the  number  of  osteoblasts  is 
smaller. 


THE    BONES. 


DEVELOPMENT  OF  SECONDARY  OR  INTERMEMBRANOUS  BONE. 

In  this  the  foundation  on  which  the  formation  of  bone  occurs  is  not 
cartilage,     but     connective    tissue. 

T       ,  ,  ,  ,,  r  .  .  Connective-tissue  bundles. 

Isolated  bundles  of  connective  tissue  . • , 


t  Osteoblast.    Calcified.  Uncalcified. 

calcify ;  on  these,  osteoblasts  de- 
rived from  embryonal  cells  arrange 
themselves  and  produce  bone  in  the 
manner  above  described  (Fig.  86). 
The  intermembranous  bone  is  en- 
closed  on  all  sides  by  connective 

,  ...  FIG.  86. — FROM  A  HORIZONTAL  SECTION  OF  THE 

tlSSUe  I     When    OSSeOUS    tissue    IS    in  PARIETAL  BONE  OF  A  HUMAN  EMBRYO.    X  240. 

Techn.  No.  62. 

direct  contact  on  one  side  with  the 

cartilage,  without  the    intervention  of   connective  tissue,    the  resulting 

formation  is  not  intermembranous,  but  perichondral  bone. 


GROWTH   OF  BONE. 

In  tubular  bones  ossification  in  the  diaphysis  begins  much  earlier 
than  in  the  epiphyses  (in  the  humerus  the  center  of  ossification  in  the 
diaphysis  appears  in  the  eighth  fetal  week,  in  the  epiphyses  in  the  first  year 
of  life)  ;  blood-vessels  grow  into  the  calcified  cartilage,  which  is  trans- 
formed at  first  only  by  endochondral,  later  also  by  perichondral,  formation 
into  bone.  The  articular  surfaces  of  the  bone  remain  permanently  cartilag- 
inous ;  a  narrow  zone  of  cartilage  between  diaphysis  and  epiphysis,  the 
epiphyseal  cartilage ',  persists  until  the  growth  of  the  bone  is  completed.  An 
active  growth  of  cartilage  is  maintained  here,  that,  by  extension  of  the 
primary  marrow-cavities  of  the  diaphysis  and  the  epiphyses,  is  continu- 
ally being  supplanted  by  bone.  In  this  way  the  bone  grows  in  length. 
Increase  in  thickness  takes  place  by  the  constant  "apposition"  of  new 
periosteal  strata. 

In  the  short  bones  ossification  takes  place,  as  in  the  epiphyses,  at  first 
by  endochondral  formation  ;  after  the  absorption  of  the  last  superficial 
remnant  of  cartilage,  a  perichondral  osseous  shell  is  formed. 

In  \\\z  flat  bones  perichondral  precedes  endochondral  formation. 

Intermembranous  bones  grow  in  superficies  and  thickness  by  the 
formation  of  new  osseous  masses  at  their  edges  and  on  their  surfaces 
respectively.  As  a  consequence  of  the  abundant  deposition  of  bone- 
substance  on  the  surface,  the  outer  and  inner  tables  of  compact  bone  are 
formed,  which  enclose  between  them  spongy  bone ;  the  latter  in  this 


152  HISTOLOGY. 

situation  is  termed  diploe.      The  osseous  masses  at  first  possess  a  coarse 
fibered,  later  (from  about  the  first  year  of  life)  a  fine-fibered  matrix. 

RESORPTION  OF  BONE. 

Immediately  following  the  initial  formation  of  osseous  tissue,  a 
contrary  process,  resorption,  becomes  perceptible,  by  which  the  calcified 
cartilage  matrix  and  many  parts  of  the  primary  and  secondary  bone 
are  removed.  Resorption  occurs  most  actively  in  the  tubular  bones  in 
the  formation  of  the  marrow-spaces,  in  a  lesser  degree  in  other  bones, 
and  on  the  surface  of  bones  until  their  typical  form  is  completed.* 

In  the  interior  of  the  compact  bone 
Giant-ceils  lying  in  Howship's  lacun.e.  irregular  excavations  may  be  seen, 

the     so-called     haversian      spaces, 
formed  by  the  absorption  of  the  in- 
Empty       nermost   haversian  lamellae,  which, 

>-     lacuna. 

however,  maybe  partly  filled  again 
by  the   deposition   of  new   osseous 
substance. 
FIG.  87.-FROM  A  CROSS-SECTION  OF  THE  HUMERUS  Wherever  resorption  of  bone 

OF  A  NEWBORN  CAT.     X   240.      H.   Haversian 

space,  containing  two  blood-vessels  and   mar-        foL-pc    nlarp      mulrin  iirlppfpd     crianf 

row-cells.     Techn.  No.  62.  IdKCb     pldCC,     IllUlllIlUCiedieU     gldlll- 

cells  may  be  seen  lying  in  pit-like 

depressions — Plows/tip's  lacuna — which  they  have  excavated  in  the  bone. 
In  this  situation  the  giant-cells  bear  the  name  of  osteoclasts  (Fig.  87). 

Even  in  the  fully-developed  skeleton  the  processes  of  apposition 
and  resorption  still  occur  at  some  places. 

TECHNIC. 

No.  57. — Ground  Sections  of  Dried  Bone. — The  bone  must  not  be 
dried  before  maceration,  but  must  be  placed  fresh  for  several  months  in 
water,  which  should  be  frequently  changed.  Then  it  is  dried,  and  a 
piece  held  between  two  pieces  of  cork  or  cloth  is  clamped  in  a  vice  and 
with  a  compass-saw  sections  i  or  2  mm.  thick,  transverse  or  longitudinal, 
are  cut.  Secure  a  section  with  sealing-wax  to  the  under  surface  of  a 
cork-stopper  (the  sealing-wax  should  also  surround  the  section),  dip  the 
whole  for  a  moment  in  water  and  then  file  it,  first  with  a  coarse,  then 
with  a  fine  file,  until  it  is  perfectly  smooth  ;  the  file  must  be  frequently 
dipped  in  water,  in  order  to  wash  off  the  adherent  particles  of  bone 
and  to  prevent  the  heating  of  the  sealing-wax  by  friction. 

The  section  of  bone  should  then  be  loosened  by  heating  the  sealing- 


*  For  example,  the  femur  of  a  three-year-old  child  contains  scarcely  any  of  the  osseous 
tissue  of  the  femur  of  the  newborn  child. 


THE    BONES.  I  53 

wax  and  the  smooth  side  stuck  fast  to  the  stopper.  It  must  now  be 
filed  until  it  is  so  thin  that  the  sealing-wax  can  be  seen  through  it.  The 
whole  should  then  be  placed  in  90  per  cent,  alcohol,  in  which  within  a 
few  minutes  the  section  becomes  loosened  from  the  cork.  Now  moisten 
a  coarse  whetstone  with  water,  rub  it  with  a  second  whetstone  until  the 
surface  is  covered  with  a  little  grinding-paste  ;  lay  the  section  in  it,  place 
a  smooth  cork  upon  it  (one  without  cracks),  and  with  a  circular  motion 
grind  it  on  both  sides  ;  it  is  not  necessary  to  glue  the  section  to  the  cork. 
The  section  when  sufficiently  thin  is  transparent  ;  this  is  to  be  ascertained 
by  drying  it  between  pieces  of  filter-paper  and  examining  with  the  low 
power.  It  should  then  be  ground  on  a  fine  whetstone,  in  the  same 
manner  as  on  the  coarse,  and  when  both  sides  are  smooth  it  should  be 
dried  with  filter-paper  and  polished.  To  do  the  latter,  nail  a  piece  of 
wash-leather  smoothly  on  a  board,  sprinkle  it  with  chalk,  and  with  the 
tip  of  the  finger  rub  the  section  to  and  fro  on  it.  In  this  way  the  pre- 
viously dull  section  acquires  shining  surfaces.  The  adherent  powder 
may  be  removed  by  rubbing  the  section  on  fresh  wash-leather.  The 
finished  section  is  to  be  placed  dry  on  a  slide  and  the  cover-glass  secured 
by  means  of  cement  (p.  45). 

Examine  first  with  the  low,  then  with  the  high  power  (Fig.  34).  If  the 
section  is  thick,  it  may  be  impossible  to  examine  it  with  the  high  power, 
since  then  the  objective  cannot  be  brought  near  enough  to  the  prepara- 
tion. The  bone  lacunae  and  bone  canaliculi  are  filled  with  air  and  with 
the  customary  illumination  of  the  object  from  below  appear  black. 

No.  5/tf. — Sharpens  Fibers. — Prepare  a  cross-section  of  the  middle 
of  the  shaft  of  a  tubular  bone,  preferably  of  a  young  individual,  accord- 
ing to  the  method  given  in  No.  56.  Place  the  finished  dry  section  for 
from  two  to  five  minutes  in  4  c.c.  of  turpentine  and  then  mount  in  damar. 
The  fibers,  invisible  in  the  sections  produced  by  other  methods  (No.  56 
and  58),  can  be  plainly  seen,  even  with  the  low  power  (Fig.  78). 

No.  58. — Haversian  Canals  and  Lamella. — Select  the  metacarpal 
bone  of  an  adult ;  after  four  weeks'  fixation  in  Miiller's  fluid,  and  hardening 
in  alcohol,  decalcify  in  nitric  acid  (p.  34),  harden  again,  and  cut  transverse 
and  longitudinal  sections.  The  compact  structure  of  larger  bones  (the 
femur,  for  example)  requires  too  much  time  (several  weeks)  for  decalcifi- 
cation.  The  periosteum  should  be  allowed  to  remain  on  the  bone.  For 
longitudinal  views  of  haversian  canals  very  thick  sections  (0.5  mm.  or 
more)  must  be  cut.  Mount  in  dilute  glycerol  (Fig.  74).  Neither  are 
very  thin  sections  necessary  for  transverse  views  and  lamellar  systems  ; 
the  lamellae  are  best  seen  if  the  section  be  examined  in  a  drop  of  distilled 
water  and  the  mirror  turned  so  that  the  object  is  only  half  illuminated  ; 
thus,  too,  the  striae  produced  by  the  bone  canaliculi,  running  vertically  to 
the  lamellae,  are  best  seen  (Fig.  75).  Mount  in  dilute  glycerol,  which, 
however,  renders  the  lamellar  systems  partially  indistinct.  Not  every 
part  of  the  bone  exhibits  all  the  lamellar  systems  ;  the  outer  and  also 
the  inner  ground  lamellae  are  frequently  wanting.  In  sections  taken 
near  the  epiphyses  the  transition  of  the  compact  substance  into  the 


154  HISTOLOGY. 

trabeculae  of  the  spongy  bone  may  be  seen.  The  bone  lacunae  and  bone 
canaliculi  are  much  less  distinct  in  moist  preparations  than  in  dried  ground 
sections,  because  the  contained  air  has  been  displaced  by  the  mounting 
medium.  (Compare  Fig.  34  with  Fig.  35.) 

Not  infrequently  the  concentric  lamellae  of  the  haversian  systems 
are  found  to  be  interrupted  by  an  irregular  line.  Up  to  this  line  the 
osseous  tissue  previously  formed  has  been  again  resorbed.  All  that  which 
lies  within  the  line  is  newly-deposited  bone-substance.  These  formations 
are,  therefore,  partially  filled  Haversian  spaces  (Fig.  75,  /i). 


G 


FIG.  88.— ISOLATED  ELEMENTS  OF  FRESH  BONE-MARROW  FROM  THE  VERTEBRA  OF  A  CALF.  X  560.  i.  In 
salt  solution.  2.  Stained  with  picrocarmine.  3.  After  treatment  with  acidulated  glycerol.  &,  Marrow- 
cells  ;  k! ',  two  marrow-cells  containing  masses  of  pigment-granules,  the  cell  on  the  right  seen  from  the 
side,  the  cell  on  the  left  from  the  surface  ;  b,  nonnucleated  colored  blood-corpuscles  ;  r,  giant-cells  ; 
in  the  one  on  the  right  the  nucleus  is  dividing  by  constriction,  and  two  of  the  future  new  nuclei  are 
seen  from  the  side,  another,  x,  from  the  surface. 


No.  59. — Red  Bone-marrow. — a.  Compress  the  vertebra  (cut  in 
half)  or  the  rib  of  a  calf  in  a  vice  or  with  tongs  ;  with  a  pipet  take  up 
a  small  drop  of  the  liquid  thus  expressed,  transfer  it  to  a  slide  and,  with- 
out the  addition  of  any  other  fluid,  apply  a  small  cover-glass  or,  better, 
a  fragment  of  a  cover-glass.  Examined  with  the  high  power  red  blood- 
corpuscles,  hematoblasts,  marrow-cells  of  different  sizes,  and  giant-cells 
will  be  seen,  but  not  always  their  nuclei  (Fig.  88,  i).  Add  a  drop  of 
picrocarmine  (p.  48) ;  the  nuclei  become  red  in  from  one  to  two  minutes, 
but  are  still  pale  (Fig.  88,  2).  If  the  picrocarmine  is  displaced  by  salt 
solution  and  then  by  dilute  acidulated  glycerol,  the  nuclei  acquire  a  deep 
color  and  sharp  contours  (Fig.  88,  3).  Occasionally  giant-cells  are 
sousrht  in  vain.  Human  ribs  are  often  usable. 

o 

b.  To  make  permanent  preparations,  proceed  as  follows  :  With  a  thin 
cover-glass  take  up  a  drop  of  the  marrow  expressed  from  a  rib  and  make 
two  cover-glass  preparations  as  directed  in  No.  39.  Since  the  marrow 
does  not  diffuse  as  readily  as  the  blood  between  the  two  cover-glasses, 
make  slight  pressure  upon  them  before  slipping  them  apart.  They  should 
not  be  allowed  to  dry,  but  should  be  placed  at  once  in  a  concentrated 
aqueous  solution  of  sublimate  solution  (5  gm.  in  100  c.c,  of  distilled 
water).  At  the  end  of  ten  minutes  transfer  the  cover-glasses  to  20  c.c. 
of  distilled  water,  which  is  to  be  changed  in  about  five  minutes.  In  ten 
minutes  place  them  in  5  c.c.  of  diluted  eosin  (p.  37,  3  £)for  from  one  to 


THE    BONES.  155 

five  minutes,  then  wash  for  a  moment  in  distilled  water  and  transfer  them 
to  5  c.c.  of  filtered  Hansen's  hematoxylin  ;  after  one  or  two  minutes 
place  them  for  five  minutes  in  distilled  water  ;  remove  the  water  by 
means  of  filter-paper  placed  at  the  edge  of  the  cover-glass  and  place 
them  in  95  per  cent,  alcohol  (not  longer  than  one  minute,  lest  the  eosin  be 
extracted),  then  in  pure  oil  of  bergamot  for  three  minutes.  With  a  cloth 
carefully  remove  the  oil  from  the  film-free  surface  of  the  cover-glass, 
place  a  drop  of  damar  on  the  surface  containing  the  film  of  marrow,  and 
invert  the  cover-glass  on  a  slide.  The  colored  blood-corpuscles  and  the 
protoplasm  of  the  hematoblasts  are  stained  a  brilliant  red,  the  protoplasm 
of  the  remaining  cells  gray-violet ;  all  the  nuclei  are  blue.  Cells  contain- 
ing oxyphile  (eosinophile)  granules  are  often  found  (Fig.  76).  Cells  with 
neutrophile  and  basophile  granules  are  obtained  by  treating  bone-marrow 
according  to  Techn.  No.  42. 

No.  60. — Articular  Cartilage. — Select  the  head  of  the  metacarpal 
bone  of  an  adult,  and  treat  it  according  to  the  method  given  in  No.  57. 
Cut  longitudinal  sections  and  mount  them  in  dilute  glycerol  (Fig.  79). 
The  parallel  streaks  often  present  in  the  hyaline  cartilage  are  produced 
by  the  razor.  The  granules  of  the  calcified  cartilage  have  disappeared 
in  consequence  of  the  process  of  decalcification  to  which  the  tissue  was 
subjected. 

No.  61. — Synovial  Villi. — From  a  cadaver,  as  fresh  as  possible,  cut 
out  a  piece  about  4  cm.  long  of  the  capsular  ligament  at  the  edge  of  the 
patella,  and  with  the  scissors  cut  a  strip  2  or  3  mm.  broad  from  the 
reddish,  glossy,  velvety  inner  surface  of  the  same,  moisten  it  with  a  drop 
of  salt  solution,  and  without  a  cover-glass  examine  it  with  the  low  power. 
At  the  edges  of  the  tissue  the  villi  may  be  seen  ;  their  blood-vessels 
often  still  contain  blood-corpuscles.  The  refractive  nuclei  of  the  endo- 
thelial  cells  lie  close  beside  one  another  (Fig.  80). 

If  it  is  desired,  the  preparation  maybe  stained  under  the  cover-glass 
with  picrocarmine  and  mounted  in  diluted  glycerol  (p.  48),  but  much  of 
the  original  beauty  is  lost. 

No.  62. — Development  of  Bone. — Human  embryos  four  or  five  months 
old,  embryos  of  the  sheep,  pig,  or  cow,  from  10  to  14  cm.  long  (measured 
from  the  tip  of  the  snout  to  the  root  of  the  tail),  are  suitable.  The  latter 
are  readily  obtained  at  the  slaughter-house  ;  the  entire  uterus  should  be 
ordered.  Place  the  embryos  in  toto  (2  or  3  in  I  liter)  in  Zenker's  fluid 
for  forty-eight  hours.  Then  wash  in  running  water  for  forty-eight  hours, 
and  harden  in  200  to  400  c.c.  of  gradually-strengthened  alcohol  (p.  33). 
After  the  embryos  have  lain  one  week  or  longer  in  90  per  cent,  alcohol, 
to  which  tincture  of  iodin  has  been  added  (p.  32),  cut  off  the  head, 
the  extremities  close  to  the  rump,  and  decalcify  them  in  200  c.c.  of 
distilled  water  to  which  2  or  4  c.c.  of  pure  nitric  acid  have  been  added. 
In  two  or  five  days,  during  which  the  decalcification  medium  must  be 
changed  about  three  times,  the  extremities  are  to  be  taken  out  (the  head 
is  probably  not  yet  decalcified,  and  must  remain  in  two  per  cent,  nitric 


I  56  HISTOLOGY. 

acid  for  several  days  longer)  and  washed  from  one  to  six  hours  in  running 
water,  and  again  hardened  in  gradually-strengthened  alcohol.  After  they 
have  lain  five  days  in  90  per  cent,  alcohol,  cut  the  extremities  into  pieces 
I  cm.  long,  which,  should  they  still  be  too  soft,  may  be  placed  for  one 
or  two  days  in  30  c.c.  of  absolute  alcohol. 

The  vertebrae  and  the  ribs  also  furnish  instructive  specimens. 

To  obtain  sections  showing  the  first  processes  in  the  development  of 
bone,  embed  in  liver  the  phalanges  and  metacarpal  bones  (the  latter  are 
very  long  in  the  animals  mentioned),  and  make  longitudinal  (sagittal)  sec- 
tions, from  the  flexor  to  the  extensor  surface  ;  to  be  good  the  sections 
must  be  taken  in  the  axis  of  the  extremities  ;  those  taken  from  the  margin 
exhibit  pictures  that  are  unintelligible. 

For  more  advanced  stages  make  chiefly  transverse  sections  of  the 
humerus  and  femur.  Sections  through  the  diaphysis  show  more  peri- 
chondral,  sections  through  the  epiphyses  more  endochondral  bone. 

The  most  beautiful  examples  of  osteoblasts  are  obtained  in  cross- 
sections  of  the  inferior  maxilla  ;  they  are  also  valuable  as  preparations 
showing  the  development  of  teeth. 

For  still  later  stages  the  skeleton  of  newborn  animals  is  useful  ; 
their  phalanges  show  tolerably  early  stages  in  the  process,  their  carpal 
bones  the  first  stages.  The  decalcification  requires  somewhat  more  time 
(up  to  eight  days). 

For  inter  me  mbranoits  bone  select  the  parietal  and  frontal  bones  of 
embryos  ;  make  horizontal  sections. 

The  sections  are  to  be  stained  in  4  c.c.  of  Hansen's  hematoxylin  for 
from  two  to  ten  minutes,  transferred  to  10  c.c.  of  distilled  water  for  ten 
minutes,  then  to  4  c.c.  of  picrocarmine  for  ten  minutes  (p.  38),  to  20  c.c. 
of  distilled  water  for  from  fifteen  minutes  to  one  hour,  and  mounted  in 
damar  (p.  45). 

If  the  staining  is  successful,  the  cartilage  (especially  the  calcified 
portions)  is  blue,  the  bone  red.  Occasionally  the  cartilage  does  not 
stain  well ;  then  place  the  sections  in  5  c.c.  of  distilled  water  plus  5  drops 
of  filtered  hematoxylin  solution.  In  from  six  to  fourteen  hours  the  carti- 
lage will  become  blue.  The  picrocarmine  staining  of  bone  often  is  not 
uniform  ;  the  youngest  portions  of  the  bone,  the  margins  of  the  osseous 
trabeculae,  for  example,  are  often  the  more  brilliantly  stained. 


IV.  THE  ORGANS  OF  THE  MUSCULAR  SYSTEM. 


The  muscular  system  is  composed  of  a  large  number  of  contractile 
organs,   the  muscles,   which  consist  of  cross-striated  muscle-tissue  and 
are  joined  to  the  skeleton,  the  skin,  the  viscera,  etc..,  by  the  intervention 
of  special  connective-tissue  for- 
mations,   the    tendons,   and     by 
accessory  apparatus    of    similar 
structure,    the    fascia,     tendon- 
sheaths,  and  bur  see. 

Each  muscle  is  composed  of 
striated  muscle-fibers,  which  as 
a  rule  are  longitudinally  dis- 
posed, so  that  they  lie  side  by 
side  and  behind  one  another,  and 
are  held  together  by  loose  con- 
nective tissue,  the  perimysium. 
Interlacing  is  rare,  but  occurs, 
for  example,  in  the  tongue. 
Neighboring  muscle-fibers  never 
are  in  direct  contact,  but  each 
individual  fiber  is  enveloped  in 
a  delicate  connective  -'tissue 
sheath,  the  perimysium  of  the 
single  muscle-fiber,  or  endomy- 
sium,  which  is  joined  to  neigh- 
boring sheaths  (Fig.  89,  /).  A  number  of  muscle-bundles  *  form  a 
muscle,  the  surface  of  which  is  covered  by  a  still  thicker  connective- 
tissue  membrane,  the  perimysium  externum,  or  epimysium.  The  several 
sheaths  are  connected  with  one  another. 

The    perimysium    is    composed    of  fibrillar   connective    tissue  and 
numerous  fine  elastic  fibers,!  occasionally  contains  fat -cells,  and  conveys 


FIG.  89.— FROM  A  CROSS-SECTION  OF  THE  ADDUCTOR 
MUSCLE  OF  A  RABBIT.  P.  Perimysium,  containing 
two  blood-vessels,  at^"/  m,  muscle-fibers  ;  many  are 
shrunken  and  between  these  the  endomysium,  p,  can 
be  seen ;  at  x  the  section  of  muscle-fiber  has  fallen 
out.  X  60.  Techn.  No.  63. 


*  The  grouping  of  the  primary  bundles  in  secondary  bundles,  that  in  a  certain  number 
of  instances  are  grouped  in  tertiary  bundles,  that  finally  unite  to  form  a  muscle,  is  an  arbitrary 
division,  and  in  many  preparations  cannot  be  recognized. 

f  In  the  epimysium  they  are  present  in  great  abundance. 

157 


58 


HISTOLOGY. 


the  nerves,  blood-vessels,  and  lymph-vessels.  The  endomysium  con- 
tains only  capillaries  and  terminal  branches  of  nerves. 

The  post-embryonal  increase  in  the  thickness  of  the  muscles  depends 
less  on  the  multiplication  than  on  the  growth  in  thickness  of  the  already 
existing  muscle-fibers. 

The  tendons  are  characterized  by  the  parallel  course  of  their  fibers,  by 
their  firm  union,  and  by  the  scarcity  of  elastic  fibers.  They  are  composed 
of  dense,  fibrous  connective-tissue  bundles,  the  "tendon-bundles,"  which 
are  held  together  by  looser  connective  tissue  and  form  the  so-called 
secondary  bundles.  Each  secondary  bundle  consists  of  a  number  of 
parallel  fibrillae  running  a  perfectly  straight  course  and  united  by  a  small 

Processes  of  tendon-cells. 
Primary  bundles. 


Loose  connect- 
ive tissue. 


Tendon- 
bundle. 


Tendon-cell. 


^  Connective    __1 . 

tissue. 
Blood- 
vessels. 


FIG.   90.— A.  FROM    A    CROSS-SECTION   OF    DRIED  TENDON    OF  ADULT  MAN.    X  5°-     Techn.  No.  64. 
B.  From  a  cross-section  of  tendon  fixed  with  chromic  acid  of  adult  man.     Techn.  No.  65. 


amount  of  cement-substance  in  so-called  primary  bundles.  Between  the 
primary  bundles  lie  the  cellular  elements  of  the  tendon,  fusiform,  stellate, 
quadrate,  or  flat  cells,  arranged  in  longitudinal  rows,  which,  curved  like 
concave  tiles,  partially  clasp  the  primary  bundles  and  unite  with  one 
another  by  means  of  processes.  Elastic  fibers  are  found  chiefly  in  the 
loose  connective  tissue  ;  in  the  dense  tendon-bundles  they  are  very  scarce 
and  occur  in  the  form  of  a  fine,  wide-meshed  network. 

The  union  of  the  muscles  with  tendons  and  fibrous  membranes 
(periosteum,  fascia)  is  effected  by  an  extension  of  the  endomysium  of  the 
muscle-fiber  into  these  structures  and  the  blending  of  the  tissues  ;  the 
sarcolemma  takes  no  part  in  this  but,  closely  investing  the  muscle- 
fiber,  terminates  as  a  closed  sheath  with  pointed  or  obliquely  blunted  ends. 


THE    ORGANS    OF    THE    MUSCULAR    SYSTEM. 


159 


The  radiating  cross-striped  muscle-fibers  in  the  skin  attach  themselves 
to  the  connective  tissue  of  the  corium  by  pointed  or  forked  ends. 

The  fascia  in  part  exhibit  the  same  structure  as  the  tendons  and  in 
part  they  are  fibrous  membranes  richly  provided  with  elastic  fibers.  The 
latter  is  the  case  when  they  form  sheaths  for  the  muscles  and  do  not 
furnish  surfaces  for  the  attachment  of  the  muscle-fibers. 

The  tendon-sheaths  and  the  bursce  consist  of  a  layer  of  connective 
tissue  and  elastic  fibers,  varying  in  thickness,  the  inner  surface  of  which 
is  covered  patch  wise  by  a  simple  stratum  of  .polygonal,  connective-tissue 
endothelial-cells.  Where  the  endothelium  is  wanting  the  connective  tis- 
sue is  dense  and  rich  in  rounded  elements  resembling  cartilage-cells. 


Elastic        LJ 

fiber.  / 


Nucleus. 


Proto- 
plasm. 


A  P, 

FIG.  91.— TENDONS    FROM    RAT'S  TAIL.        X   240.      A.  Tendon-cell        FIG.    92.-FRoM    A    SAGITTAL 
viewed  in  profile.     B.  From  the  surface.    At  X  the  nucleus  is  bent  LONGITUDINAL  SECTION    OF 

so  that  it  is  seen  partly  in  profile  (the  shaded  portion)  and  partly  THE  GASTROCNEMIUSOF  THE 

from  the  surface  (the  light  portion).     Techn.  No.  65.  FROG.      Xso.      The   upper- 

most transverse  line  repre- 
sents the  perimysium  seen 
from  the  surface.  Techn. 
No.  67. 

The  majority  of  the  tendon-sheaths  have  small  vascular  processes  ex- 
actly like  the  synovial  fringes. 

The  blood-vessels  of  striated  muscles  are  very  numerous  and  evenly 
distributed  ;  the  capillaries  are  among  the  thinnest  in  the  human  body 
and  form  networks  characterized  by  elongated  rectangular  meshes, 
closely  surrounding  the  individual  fibers.  The  veins  are  provided 
with  valves  even  in  their  smallest  branches.  The  lymph-vessels  are  few 
in  number  and  follow  the  ramifications  of  the  smaller  blood-vessels. 

For  the  nerves,  partly  sensory  and  partly  motor,  of  cross-striped 
muscle  see  the  Peripheral  Nerve -endings. 

The  blood-vessels  of  the  tendons  and  the  thinner  fasciae  are  very 
scarce,  and  are  contained  only  in  the  loose  connective  tissue  surrounding 


l6o  HISTOLOGY. 

the  tendon-bundles  ;  the  tendon-sheaths  and  the  bursae  have  a  rich  vas- 
cular supply.  Lymph-vessels  are  found  only  on  the  surface  of  the  tendons. 
The  medullated  nerves  of  tendons  terminate  in  part  in  a  close  plexus 
of  gray  nerve-fibers  and  in  part  pass  into  spindle-shaped  expansions  of 
the  tendon,  the  so-called  tendon-spindles,  where  they  end  in  structures 
resembling,  but  more  richly  branched  than,  the  motorial  end-plates. 
End-bulbs  and  Pacinian  corpuscles  are  found  in  tendons,  fasciae,  and 
tendon-sheaths. 

TECHNIC. 

No.  63. — Bundles  of  Striped  Muscle. — Select  a  muscle  in  which  the 
fibers  have  a  parallel  disposition  (for  example,  the  adductor  of  the  rab- 
bit) and  with  a  sharp  razor  make  a  deep  incision  transverse  to  the  course 
of  the  fibers  and  2  or  3  cm.  below  a  second  incision  ;  connect  these  by 
longitudinal  incisions  and,  without  traction,  carefully  remove  the  piece 
thus  mapped  out.  For  fixation  place  it  in  100  c.c.  of  o.  I  per  cent, 
chromic  acid  (p.  31).  After  two  weeks  wash  it  in  running  water  and 
harden  in  50  c.c.  of  gradually-strengthened  alcohol  (p.  33).  Cut  cross- 
sections  and  examine  them  unstained  in  diluted  glycerol  (Fig.  89).  The 
muscle-fibers  vary  greatly  in  thickness  ;  the  smallest  are  sections  through 
the  ends  of  the  fibers.  Although  the  muscle-fibers  are  cylindrical  and 
should  therefore  in  section  appear  circular,  they  have  an  irregularly 
polygonal  outline  due  to  mutual  pressure.  The  color  of  the  sections  is 
very  different,  some  are  quite  dark,  others  quite  clear.  The  cause  of  this 
phenomenon  is  unknown  to  me.  The  endomysium  is  best  seen  with  the 
high  power  (240  diameters). 

No.  64. — Tendons. — Cut  from  a  tendon  a  piece  5  or  10  cm.  long, 
and  let  it  dry  in  the  air  (but  not  in  the  sun).  Thin  tendons  (e.  g.,  that 
of  the  flexor  digitorum  pedis)  at  room-temperature  are  sufficiently  dry 
in  twenty-four  hours.  Thicker  tendons  require  several  days.  With  the 
scalpel  (not  the  razor)  cut  a  smooth  transverse  surface  and  then  cut  thin 
shavings  from  the  tendon,  supporting  it  on  the  thumb  of  the  right  hand  and 
with  the  remaining  fingers  grasping  the  scalpel  (the  manipulation  is  the 
same  as  in  sharpening  a  pencil).  Throw  the  shavings  into  a  capsule  con- 
taining distilled  water  and  in  two  minutes  examine  in  a  drop  of  the 
same  medium  (Fig.  90,  A).  To  preserve,  stain  in  3  c.c.  of  picrocarmine 
for  five  minutes  and  mount  in  dilute  glycerol.  Very  frequently  a  streak 
may  be  seen  extending  across  the  entire  section  ;  this  is  produced  by 
the  knife. 

Place  another  section,  unstained,  in  a  drop  of  water  on  a  slide  ; 
treat  it  under  the  cover-glass  with  a  drop  of  acetic  acid  ;  the  edge  of  the 
section  soon  exhibits  swollen  convoluted  bands  (acetic-acid  reaction  of 
connective  tissue). 

No.  65. — For  the  study  of  the  minute  structure  of  tendon,  its  cells 
and  their  processes,  place  a  thin  tendon,,  as  fresh  as  possible  (that  of  the 


THE    ORGANS    OF    THE    MUSCULAR    SYSTEM.  l6l 

palmaris  longus  muscle),  in  pieces  3  cm.  long  in  100  c.c.  of  0.5  per  cent, 
chromic  acid  for  at  least  four  weeks.  The  chromic  acid  should  be  changed 
several  times  during  this  period.  Then  wash  the  tissue  in  running  water 
one  or  two  hours  and  harden  it  in  about  40  c.c.  of  'gradually-strength- 
ened alcohol  (p.  33).  The  sections  should  be  cut  with  a  very  sharp 
razor ;  often  the  tendon  is  so  brittle  that  it  falls  to  pieces  in  cutting. 
The  sections  need  not  be  very  thin.  Mount  them  unstained  in  diluted 
glycerol.  Examined  with  the  low  power  and  reflected  light  (with  the 
mirror  muffled)  they  yield  beautiful  pictures,  better  than  the  preparations 
made  like  Techn.  No.  63.  With  the  high  power  they  resemble  Fig.  90, 
B.  The  black  zigzag  spaces  are  partly  occupied  by  tendon-cells. 

No.  66. — Tendon-cells. — From  the  tail  of  a  rat  or  mouse  cut  pieces 
of  tendon  from  0.5  to  I  cm.  long  and  place  them  in  5  c.c.  of  alum-carmine. 
The  following  day  (or  later)  transfer  the  swollen  pieces  to  a  dry  slide 
and  rapidly  tease  them  (p.  28).  It  is  not  necessary  to  separate  the 
tendon  into  very  small  bundles,  but  care  should  be  taken  that  the  bundles 
lie  straight.  Then  cover  the  preparation  with  a  drop  of  distilled  water 
and  a  cover-glass.  With  the  low  power  the  rows  of  cells  appear  for  the 
most  part  as  dark  streaks  ;  they  are  the  cell-nuclei  seen  in  profile.  In 
surface  views  the  nuclei  appear  dull  red.  The  body  of  the  cells,  the  pro- 
toplasm, can  only  be  seen  with  the  high  power ;  viewed  laterally,  it 
appears  as  a  sharp,  dark  streak  (Fig.  91,  A)  ;  from  the  surface,  paler  and 
delicate  (Fig.  91,  B).  Not  infrequently  the  cells  are  folded,  so  that  they 
are  visible  partly  from  the  edge  and  partly  from  the  surface.  The  connec- 
tive-tissue fibers  may  be  occasionally  distinguished  as  delicate  parallel 
lines  ;  the  fine  elastic  fibers  with  their  sharp  contours  are  always  distinct. 
The  focus  should  be  changed  by  means  of  the  micrometer-screw,  and  the 
different  planes  of  the  section  examined.  If  the  cells  are  not  distinct  add 
a  drop  of  acetic  acid  (p.  48).  To  preserve,  displace  the  water  with 
diluted  glycerol. 

No.  67. — Muscle  and  Tendon. — Remove  the  skin  from  the  hind  leg 
of  a  frog  just  killed,  and  with  scissors  cut  off  the  leg  above  the  knee- 
joint,  just  above  the  origin  of  the  gastrocnemius.  Fix  it  in  50  c.c. 
of  Kleinenberg's  picrosulphuric  acid  (p.  21).  After  twenty-four  hours 
transfer  it  directly  to  50  c.c.  of  70  per  cent,  alcohol  for  gradual 
hardening.  In  about  six  days  cut  off  the  muscle  with  a  piece  of  the 
tendo-Achillis,  and  stain  it  in  bulk  in  borax-carmine  (p.  37).  Then  harden 
again  in  90  per  cent,  alcohol.  Cut  sagittal  longitudinal  sections,  placing 
the  razor  first  on  the  tendon  occurring  on  the  posterior  surface  of  the 
muscle.  Mount  in  damar  (p.  45).  Very  often  not  a  trace  of  the  cross- 
striation  of  the  muscle-fibers  is  to  be  seen  (Fig.  92). 


ii 


V.  THE  ORGANS  OF  THE  NERVOUS  SYSTEM. 

I.  THE  CENTRAL  NERVOUS   SYSTEM.* 

THE  SPINAL  CORD. 

Typography. — The  spinal  cord  consists  of  a  white  and  a  gray  sub- 
stance, that  are  distinguishable  by  the  unaided  eye.  The  arrangement 
and  the  relation  of  these  substances  are  best  recognized  in  cross-sections 
of  the  spinal  cord. 

The  white  substance  encircles  the  gray  substance,  and  is  partially 
divided  by  a  deep  anterior  cleft,  the  anterior  median  fissure,  and  a  poste- 
rior septum  (formerly  called  the  posterior  median  fissure)  into  a  right  and 
a  left  half.  *  Each  half  is  subdivided  by  the  furrows  marking  the  exit  of 
the  anterior  and  the  posterior  roots  of  the  spinal  nerves  into  a  large  lateral 
column,  an  anterior  column,  and  a  posterior  column.  In  the  lower  cervical 
and  the  upper  thoracic  regions  two  divisions  may  be  distinguished  in  the 
posterior  column,  of  which  the  median  portion  is  named  the  column  of 
Goll  (funiculus  gracilis)  and  the  lateral  portion  the  column  of  BurdacJi 
(funiculus  cuneatus).  The  anterior  columns  are  united  by  the  w J lit e  com- 
missure at  the  bottom  of  the  anterior  median  fissure. 

The  gray  substance  in  cross-section  appears  in  the  form  of  an  H 
and  in  its  entirety  consists  of  two  lateral  columns,  which  are  connected 
by  a  horizontal  lamella,  the  gray  commissure.  On  each  column  thick 
anterior  cornua  and  slender  posterior  cornua  may  be  distinguished. 
Adjoining  the  lateral  portions  of  the  anterior  horns,  in  the  same  frontal 
plane  with  the  central  canal,  are  the  lateral  cornua,  which  are  especially 
well  developed  in  the  upper  thoracic  region.  From  the  front  boundary 
of  the  anterior  cornua  the  anterior  roots  of  the  spinal  nerves  emerge  in 
several  bundles,  while  the  posterior  roots  enter  at  the  postero-median  side 

*  I  shall  confine  myself  here  to  a  brief  account  of  the  topography  and  histology  of  the 
spinal  cord  and  the  brain.  An  exhaustive  presentation  of  the  architecture  of  the  central  nervous 
system,  the  paths  of  the  nerve-fibers,  and  the  complicated  origins  of  the  cranial  nerves  in  the 
"nuclei"  of  the  oblongata  would  exceed  the  limits  of  this  "Histology."  The  student  is 
referred  to  special  text-books,  of  which  Edinger's  "  Vorlesungen  liber  den  Bau  der  nervosen 
Centralorgane  "  is  recommended. 

162 


THE    CENTRAL    NERVOUS    SYSTEM. 


163 


of  the  posterior  cornua.  Laterally,  at  the  base  of  the  posterior  cornua, 
a  net-like  mass  of  gray  substance,  the  reticular  process  (formatio  reticu- 
laris),  is  found  ;  at  the  median  side  of  the  posterior  horn,  near  the  gray 
commissure,  lies  the  column  of  Clarke  (dorsal  nucleus),  well  defined  in 
the  whole  length  of  the  thoracic  and  in  the  upper  part  of  the  lumbar 
region  of  the  cord.  At  the  summit  of  the  posterior  horns  a  glistening, 
jelly-like  mass,  macroscopically  easily  perceptible,  the  substantia  gelatinosa 
(Rolando),  may  be  distinguished.  Posteriorly  to  this  is  the  small  zona 
spongiosa,  at  the  dorsal  edge  of  which  is  found  the  border  zone,  zona 


Posterior  column. 


^    Entrance  of 
posterior 
root-fibers. 


Lateral 
column. 


ZS.4  Anterior 
horn. 


Lateral  posterior,  / 

/ 
Medial  anterior 

Groups  of  nerve-cells. 


White  com- 
missure. 


Gray  commissure  within 
which  is  the  central 
canal. 


FIG.  93.— CROSS-SECTION  OF  THE  CERVICAL  ENLARGEMENT  OF  THE  HUMAN  SPINAL  CORD.    X  7. 

Techn.  No.  67. 

terminalis,  an  area  of  cross-sectioned  thin  nerve-fibers.  In  the  gray 
commissure  lies  the  cross-section  of  the  central  canal,  which  extends 
through  the  whole  length  of  the  spinal  cord  and  is  surrounded  by  the 
substantia  grisea  centralis.  The  central  canal  is  from  0.5  to  I  mm.  in 
diameter  ;  not  infrequently  it  is  obliterated.  The  portions  of  the  gray 
commissure  in  front  of  and  behind  the  central  canal  are  respectively  named 
anterior  and  posterior  gray  commissure.  In  man  the  latter  is  the  smaller. 
From  the  entire  periphery  of  the  gray  substance  coarser  or  finer  pro- 
cesses, the  septula  mcdullaria,  radiate  into  the  white  substance.  In  the 
cervical  and  lumbar  enlargements  of  the  spinal  cord  the  gray  matter  is 


164  HISTOLOGY. 

more  powerfully  developed  than  in  the  thoracic  region  ;  there  is  a  corre- 
sponding variation  in  the  form  of  the  H.  The  end  of  the  conus  mcdnllaris 
consists  almost  wholly  of  gray  substance. 

Minute  Structure. — The  gray  substance  will  be  first  considered,  a 
knowledge  of  its  composition  being  essential  to  the  comprehension  of 
the  structure  of  the  white  substance.  The  gray  substance  consists  of 
multipolar  nerve  (ganglion)-cells,  that  with  their  dendrites  and  nerve- 
processes  form  a  dense  nervous  tangle,  the  "  nerve-felt  "  (neuropilem). 
This  felt  is  penetrated  by  nerve-fibers,  partly  proceeding  from  the  white 
columns,  partly  from  the  posterior  roots  ;  the  whole  is  supported  by 
a  framework  of  neuroglia. 

We  have  to  consider  first  the  nerve-cells,  then  the  nerve-fibers  ;  the 
neuroglia,  which  also  occurs  in  the  white  substance,  will  be  described  at 
the  conclusion  of  the  entire  recital. 

The  nerve-cells,  in  accordance  with  the  relations  and  distribution  of 
their  nerve-process,  are  divided  into(i)  motor  cells,  (2)  column-cells,  and 
(3)  internal  cells.* 

The  motor  nerve-cells  (rhizoneurons)  lie  in  two  groups  f  in  the  ante- 
rior horn.  They  possess  a  large  cell-body  (67  to  135  //.)  and  long  den- 
drites, extending  far  into  the  surrounding  substance  ;  the  nerve-process 
emerges  from  the  summit  of  the  anterior  cornu,  makes  an  oblique  descent 
through  the  white  substance,  at  the  same  time  receives  a  medullary 
sheath  and  becomes  the  axis-cylinder  of  a  medullated  nerve -fiber. 
Occasionally  the  axis-cylinder  process  gives  off  a  few  insignificant  lateral 


*  Editor's  remark  :  A  classification  and  nomenclature  based  upon  the  behavior  and  dis- 
tribution of  the  axis-cylinder  have  recently  been  suggested  in  America,  that,  in  many  respects, 
appear  to  me  to  be  appropriate  and  natural,  and  have  been  widely  accepted.  According  to  this 
two  chief  groups  are  distinguished,  namely  :  I,  axoneurons,  and,  II,  ganglioneurons. 

I.  The  axoneurons  embrace  all  those  neurons  the  cell-body  (nerve-cell)  of  which  lies  in 
the  interior  of  the  spinal  cord  or  the  brain.     Corresponding  to  the  different  behavior  of  the  nerve- 
process,  they  are  further  divided  into  two  subordinate  groups,  namely : 

(a)  Rhizoneurons,  the  nerve-process  of  which  leaves  the  spinal  cord  through  the  anterior 
root  (they  comprise  the  motor  nerve-cells),  and — 

(b]  Endaxoneurons,  the  nerve-process  of  which  does  not  leave  the  spinal  cord.     Among 
these  we  may  distinguish  (l)  those   the  nerve-process  of  which  enters  the  different  columns  of 
the  white  substance  (column-cells],  and  (2)  those  the  nerve-process  of  which  within  the  gray 
substance  rapidly  breaks  up  into  its  terminal  ramifications  (internal  cells]. 

II.  The  ganglioneurons  represent  those  neurons  the  cell-body  of  which  lies  within  the 
spinal  ganglia  or  the  cerebral  ganglia  and  that  stand  in  connection  with  the  central  nervous  sys- 
tem only  by  means  of  their  central  process. 

f  An  antero-median  and  postero-lateral  group,  separate  in  the  cervical  and  lumbar  enlarge- 
ments, but  in  the  uppermost  cervical  and  in  the  thoracic  regions  united  in  a  single  cluster  (P'ig.  93). 
In  longitudinal  sections  it  may  be  seen  (conspicuously  in  amphibians)  that  the  cell  groups,  gov- 
erned by  the  origin  of  the  single  roots,  have  a  correspondingly  typical  segmental  arrangement. 


THE    CENTRAL    NERVOUS    SYSTEM. 


I65 


twigs  (collaterals)  before  leaving  the  gray  matter.  It  leaves  as  a  con- 
stituent part  of  an  anterior  (ventral)  root-fiber  bundle  of  the  spinal 
cord.  All  anterior  root-fibers  arise  from  the  motor  cells  of  the  anterior 
horn,  from  those  of  the  same,  not  the  opposite,  side. 

The  column-cells  (Stmngzellen,  endaxoneurons)  constitute  the  chief 
mass  of  the  nerve-cells  of  the  gray  substance,  and  in  this  lie  everywhere 
(except  in  the  places  occupied  by  the  motor  nerve-cells),  partly  scattered, 
partly  in  groups  in  the  lateral  '  horn  and  in  the  dorsal  nucleus.  The 
majority  are  smaller  than  the  motor  nerve -cells  and  possess  few,  little- 
branched,  but  far-reaching  dendrites.  Their  nerve -process,  after  sending 


FIG.  94.— Two  FORMS  OF  MOTOR  NERVE-CELLS  FROM  THE  ANTERIOR  HORN  OF  THE  SPINAL  COR£>  OF 
A  RABBIT.    «.  Nerve-process.     X  60.     Techn.  No.  70.    (Schaper.) 

off  numerous  collaterals  in  the  gray  substance,  enters  the  white  substance 
— in  the  anterior  or  lateral  column,  very  rarely  the  posterior  column — 
either  on  the  same  or  on  the  opposite  side.  Cells  of  the  latter  kind  are 
sometimes  termed  commissure -cells*  because  the  nerve -process  passes 
through  the  anterior  gray  commissure  before  entering  the  white  substance. 
Having  arrived  in  the  white  substance,  the  nerve -process  of  the  majority 


*  The  commissure-cells  occupy  an  area  which,  arch-like,  embraces  the  central  canal  on 
the  ventral  side ;  there  they  are  of  conspicuous  size,  approaching  that  of  the  motor  cells  of  the 
anterior  horns.  Also  farther  back,  in  the  median  division  of  the  gray  substance,  scattered  com- 
missure-cells occur,  but  they  are  wanting  in  the  posterior  horns. 


1 66 


HISTOLOGY. 


of  the  column-cells  *  divides  into  a  vertical  ascending  and  descending 
"  stem -fiber,"  that  in  its  course  parallel  to  the  longitudinal  axis  of  the 
spinal  cord  sends  off  lateral  twigs  (collateral  fibers),  which  return  to  the 
gray  substance,  where  they  terminate  in  tufts  of  free  fibrils  ;  the  stem- 
fibers  themselves  finally  terminate  like  the  collateral  fibers.  The  col- 
lateral fibers  that  enter  from  the  anterior  columns  penetrate  the  anterior 
cornua  singly  or  in  bundles,  where  they  weave  a  net  around  the  large 
motor  cells  ;  they  are  especially  numerous  in  the  antero-lateral  curve  of 
the  anterior  horn  ;  not  less  numerous  are  the  collateral  fibers  coming 
from  the  lateral  columns.  The  spindle-shaped  "  marginal  cells  "  lying 
in  the  zona  spongiosa  also  belong  to  the  column-cells.  In  the  adult,  all 


Posterior  root. 


Lateral  column-cell  with  _ 


Central  canal. 


Motor  cell  of  the  lateral 
posterior  group. 


Nerve-process. 
Gray  matter. 


White  matter V-        \ 


Commissure-cell. 

Nerve-processes. 

FIG.  95.— CROSS-SECTION  OF  THE  SPINAL  CORD  OF  A  SEVEN-DAY-OLD  EMBRYO  CHICK.       X  80. 
white  matter  is  but  slightly  developed,  the  central  canal  is  still  very  large.    Techn.  No.  70. 


The 


the  nerve-processes   of  the  column-cells  are  enveloped  in  a  medullary 
sheath. 

The  cells  so  far  described  are  characterized  by  their  long  nerve- 
process  ;  they  belong  to  the  nerve-cells  of  the  first  type  (Deiters's). 
.There  is  another  kind  of  cell,  the  nerve-process  of  which  rapidly  divides 
and  remains  within  the  gray  substance.  Because  they  do  not  pass  beyond 
the  gray  substance  these  elements  are  named  internal  cells  ;  they  occur 


*  The  nerve-processes  coming  from  the  vesicular  column  of  Clarke  do  not  divide  in  the 
white  substance,  but  turn  cranialward  and  proceed  to  the  cerebellum.  The  nerve-processes  of 
still  other  column-cells  enter  the  white  substance,  and  there  without  dividing,  turn  upward  or 
downward.  Under  the  name  of  "  plurifunicular  cells  "  column-cells  have  been  described,  the 
nerve-process  of  which  divides  in  the  gray  substance  into  two  or  three  branches  and  continues 
in  as  many  fibers  in  different  columns. 


THE    CENTRAL    NERVOUS    SYSTEM. 


i67 


in  the  posterior  columns,  where  their  terminal  ramification  spreads  out 
either  on  the  same  or  on  the  opposite  half  of  the  spinal  cord.  They  are 
nerve-cells  of  the  second  type  (Golgi's)  (Fig.  96). 

The  nerve-fibers  that  enter  from  the  anterior  and  lateral  columns 
partly  arise  from  the  medullated  collateral  fibers  and  ends  of  the 
nerve-processes  of  the  column-cells,  partly  from  the  nerve-processes 
(likewise  invested  by  a  medullary  sheath)  that  come  from  the  brain.*  In 


Motor  cell. 


Commissure-cell. 
Column-cell. 


Internal  cell. 


Collaterals. 


Ascending  fiber. 


Spinal  ganglion-cell. 


Descending  fiber. 


FIG.  96.— SCHEME  SHOWING  THE  LOCATION  AND  RAMIFICATION  OF  THE  NERVE-CELLS,  ALSO  OF  THE 
POSTERIOR  NERVE-ROOTS  OF  THE  SPINAL  CORD. 

addition  there  are  medullated  nerve-fibers  of  the  posterior  (dorsal)  roots 
which  originate  in  the  centripetal  processes  of  the  cells  of  the  spinal 
ganglia.  These  posterior  root-fibers  enter  the  spinal  cord  in  two  groups, 
a  lateral,  which  runs  in  the  zona  terminalis,  and  a  larger  median,  which 
runs  in  the  posterior  column.  These  fibers  do  not  directly  enter  the  gray 


*  For  an  account  of  the  exact  course  of  these  fibers  the  student  is  referred  to  special  text- 
books. 


i68 


HISTOLOGY. 


substance,  but  each  first  divides  Y-shape  into  an  ascending  and  descend- 
ing stem-fiber  (Fig.  97),  from  which  numerous  collateral  fibers  diverge  at 
right  angles.  These  now  enter  the  gray  substance  *  and  with  their  tufts 
of  terminal  fibrils  distribute  themselves  over  nearly  every  point  of  the 
same.  One  set  terminates  principally  in  the  summit  of  the  posterior 
horn  ;  these  take  their  origin  in  the  lateral  root-fiber  group  and  form  a 
very  fine-fibered  dense  plexus,  that  also  partly  lies  in  the  substantia  gela- 
tinosa  (Fig.  98,  c) ;  a  second  set  terminates  in  the  dorsal  nucleus  (Fig. 
98,  a)  ;  f  these  originate  in  the  median  root-fiber  group,  as  also  a  third 
set,  which  penetrating  the  middle  of  the  substantia  gelatinosa  passes  ven- 
tral ward  into  the  anterior  horn  and  there  radiating  fan-shape  surrounds- 
the  motor  nerve-cells  (Fig.  98,  U)  ;  these  'latter  very  robust  collateral 

fibers  ("  reflex  collaterals  ")  arise 
from  the  portion  of  the  stem-fibers 
close  to  the  point  of  bifurcation  and 
form  the  reflex  bundle.  %  Finally,  a 
fourth,  smaller  set  of  collateral  fibers 
passes  through  the  posterior  gray 
commissure  to  the  posterior  horn  of 
the  opposite  side.  The  stem-fibers, 
probably  only  after  a  long  course, 
sometimes  extending  into  the  oblon- 
gata,  turn  into  the  gray  substance, 
where  they  terminate  like  the  col- 
laterals. 

The  peculiarities  of  the  sub- 
stantia grisea  centralis  and  substantia 
gelatinosa,  which  belong  to  the  gray 

substance,  are   dependent  upon  the  abundance  of  neuroglia  and  will  be 
described  with  this. 

The  white  substance  consists  only  of  medullated  nerve-fibers,  that 
do  not  possess  a  neurilemma.  The  fibers  differ  greatly  in  thickness  ;  the 
thickest  are  found  in  the  anterior  columns  and  in  the  lateral  parts  of  the 


Ascending  stem- 
fiber. 


Descending  stem 

fiber. 


Nerve-fibers  of 
posterior  root. 


FIG.  97. — FROM  A  LONGITUDINAL  SECTION  OF 
THE  SPINAL  CORD  OF  A  NEWBORN  RAT.  X 
no.  The  section  shows  two  posterior  nerve- 
roots.  The  collateral  fibers  are  not  visible. 
Techn.  No.  70. 


*  An  exception  occur?  in  the  case  of  some  fiber-bundles  which  directly  enter  into  the 
gelatinous  subsance  and  partly  in  this  or  ventral  thereto  (in  the  territory  of  the  posterior  horn) 
divide  into  ascending  and  descending  stem-fibers. 

•j-  Here  the  medullary  sheaths  extend  farther  than  elsewhere, — that  is,  to  the  last  terminal 
ramification. 

J  The  reflex  bundle  and  the  collateral  fibers  of  Clarke's  column  sink  into  the  gray 
substance  in  a  curve  with  the  concavity  lateralward  and  form  a  considerable  mass  easily  per- 
ceived. The  place  at  which  they  enter  the  gray  substance  has  been  named  "  root-entrance  zone." 


THE    CENTRAL    NERVOUS    SYSTEM. 


169 


posterior  columns  ;  the  thinnest  in  the  median  part  of  the  posterior 
columns  and  in  the  lateral  columns  where  the  white  touches  the  gray 
substance.  In  the  remaining  portions  thick  and  thin  fibers  are  inter- 
mingled. The  majority  of  the  nerve-fibers  run  parallel  with  the  long  axis 
of  the  spinal  cord,  hence  in  cross-sections  are  cut  transversely.  In 
addition  there  are  fibers  that  take  an  oblique  direction  ;  these  are  found 
in  large  numbers  in  front  of  the  gray  commissure,  where  they  cross  at 
acute  angles  and  form  the  white  commissure  (Fig.  93). 

An  attempt  to  classify  the  nerve-fibers  according  to  their  origin  will 


Anterior 
horn. 


Glia-cells 


Blood-vessels. 


Collateral  fiber  of  a  column-cell. 


FIG.  98.— CROSS-SECTION   OF  THE  SPINAL  CORD  OF  A  NEWBORN  RAT  SHOWING  COLLATERAL  FIBERS. 
X  75-    In  the  right  half  only  one  representative  of  each  class  has  been  sketched.    Techn.  No.  70. 


result  as  follows  :  i,  fibers  which  are  continuations  of  the  posterior  root ; 
the  entire  posterior  column  consists  of  posterior  root-fibers,  because  the 
latter  (or  their  stem-fibers),  entering  in  the  lumbar  region,  are  pushed 
toward  the  median  line  by  the  fibers  entering  at  higher  levels  ;  2,  fibers 
which  are  continuations  of  the  column-cells  ;  3,  fibers  which  are  continua- 
tions of  the  ganglion-cells  of  the  brain.  The  latter  two  occupy  the 
anterior  and  lateral  columns  and  are  united  in  compact  bundles  (funiculi). 
The  supporting  framework  of  the  spinal  cord  is  constructed  of  two 
genetically  distinct  formations  :  I,  connective-tissue  extensions  of  the  pia, 
which  penetrate  the  white  substance  as  sheaths  for  the  blood-vessels  ; 


1 7<D  HISTOLOGY. 

this  mesenchymal  framework  steadily  grows  thinner  as  it  approaches  the 
gray  substance,  into  which  it  does  not  extend  ;  2,  the  nenroglia  ("  nerve- 
cement "),  which  is  derived  from  the  same  embryonic  anlage  as  the  cen- 
tral nervous  system.  The  neuroglia  principally  consists  of  nucleated 
elements,  the  glia-cells,  and,  possibly,  of  a  small  amount  of  homogeneous 
ground-substance.  There  are  two  kinds  of  glia-cells,  ependymal  cells 
and  astrocytes.  The  ependymal  cells  in  a  single  layer  line  the  lumen 
of  the  central  canal.  In  youth  they  are  beset  with  cilia,  their  cylin- 
drical bodies  are  prolonged  in  an  extended  process  that  in  the  embryo 
reaches  to  the  surface  of  the  spinal  cord,  where  it  terminates  in  a  simple 


From  the  substantia  gelatinosa  of  a  newborn  rat. 

Glia'ce"- 


Central  canal.  —. 


Ependymal  cells. 


Concentrically-arranged  glia-cells 
from  a  six-week-old  cat. 


Glia-cell  of  gray  matter  of  the  base  of  the 
posterior  horn  of  a  human  embryo. 


FIG.  99.— GLIA-CELLS  FROM  THE  SPINAL  CORD.    X  280.  Techn.  No.  70. 

or  branched  end  (Fig.  99).  The  cells  of  the  ependyma  are  phylogeneti- 
cally  the  older  ;  they  arise  also  ontogenetically  first,  but  in  the  further 
course  of  development  undergo  regression  in  different  degrees  ;  the  long 
processes  in  particular  are  involved,  which  retain  their  original  length,  to 
the  surface  of  the  spinal  cord,  only  in  the  region  of  the  posterior  median 
septum*  and  opposite,  to  the  base  of  the  anterior  median  fissure.  In  the 
course  of  development  one  division  of  the  ependymal  cells  wanders  per- 
ipheryward  and  becomes  transformed  into  astrocytes.  Not  infrequently 

*The  posterior  median  septum  consists  for  the  greater  part  of  processes  of  ependymal  cells. 


THE    CENTRAL    NERVOUS    SYSTEM. 


I/I 


White  matter.     Hornspongiosa. 


the  central  canal  is  completely  obliterated.  The  astrocytes  (Deiters's  cells), 
in  the  beginning  of  their  development  lie  in  the  gray  substance  ;  later  they 
retreat  into  the  white  substance  and  then  are  very  differently  shaped. 
Of  the  numerous  processes  of  the  astrocytes  one,  the  "  chief  process," 
frequently  originates  first ;  the  others,  partly  finer  and  partly  coarser 
"secondary"  processes,  arise  later.  Many  of  these  cells,  with  much- 
branched  processes,  reach  to  the  surface  of  the  spinal  cord,  where  they 
terminate  in  expanded  ends  *  and  form  a  distinct  border  on  the  superficial 
glia-zone,  the  "gelatinous  cortical  layer"  or  "  hornspongiosa."  Two 
varieties  of  the  developed  cells,  united  by  many  transitional  forms,  may 
be  distinguished :  the  mossy-cells 
and  the  spider-cells.  The  mossy- 
cells  possess  shorter,  very  richly- 
branched  processes,  that  not  in- 
frequently are  applied  to  the 
blood-vessels  ;  they  chiefly  occur 
in  the  gray  substance  ;  the  spider- 
cells,  the  more  usual  form,  have  a 
small  cell-body  from  which,  be- 
sides short,  also  many  longer, 
rigid,  less-branched  processes  radi- 
ate (like  Fig.  104) ;  these  chiefly 
occur  in  the  white  substance  and 
are  not  apt  to  be  confused  with  the 
ganglion-cells.  By  the  interlacing 
of  the  numerous  fine  processes  of 
neighboring  glia-cells  (they  do  not 
anastomose)  a  close  web  is  con- 
structed which  envelops  each  indi- 
vidual nerve-fiber. 

In  the  substantia  grisea  centralis  and  substantia  gelatinosa  the 
neuroglia  assumes  a  totally  different  appearance.  In  the  former  the 
astrocytes,  with  their  here  very  long,  stiff,  unbranched  processes,  are 
concentrically  arranged  in  a  fiber-wreath  (Fig.  99).  These  and  the  cells 
of  the  ependyma  are  together  called  "central  ependyma  filaments." 
The  substantia  gelatinosa  consists  of  a  small  number  of  very  small 
ganglion-cells,  the  nerve-processes  of  which  turn  into  the  zona  ter- 


Cross  -  sections 

.     of  medullated 

nerve-fib  e  r  s 
consisting 
of— 


Axis-cylinder 
and 

*\Medullary 

sheath. 


Glia-cells. 


XCon 


ective 
tissue. 


Blood-vessels. 


FIG.  JOG.— FROM  A  CROSS-SECTION  OF  THE  HUMAN 
SPINAL  CORD  IN  THE  REGION  OF  THE  LATERAL 
COLUMN.  X  180.  Techn.  No.  69. 


*  These  expanded  ends  stand  close  beside  one  another,  and  form  a  "  membrana  limitans 
meningea,"  that  is  not  an  independent  membrane  any  more  than  the  internal  limiting  mem- 
brane of  the  retina  (see  The  Eye  and  its  Appendages.) 


I/2  HISTOLOGY. 

minalis,  of  a  plexus  of  delicate  nerve-fibrils,  and  of  nerve-fibers  (collat- 
erals) passing  through  ;  there  is  besides  a  granular  substance  present 
which  has  arisen  by  a  transformation  of  numerous  and  very  delicate 
processes  of  the  astrocytes  occurring  there. 

THE    BRAIN. 

The  brain,  like  the  spinal  cord,  is  composed  of  a  white  and  a  gray 
substance,  which  in  their  minute  structure  agree  on  the  whole  with  the  same 
substances  in  the  cord.  But  the  arrangement  of  the  two  substances  in 
the  brain  is  a  much  more  diversified  one  than  in  the  spinal  cord. 

The  gray  substance  of  the  brain  occurs  in  four  aggregations  : 

(a)  As  the  cerebral  cortex,  an  expansion  covering  the  entire  surface 
of  the  cerebral  hemispheres. 

(&)  In  the  form  of  discrete  masses,  which  are  situated  in  the  cerebral 
ganglia, — the  corpora  striata,  the  optic  thalami,  the  corpora  quadrigemina. 

(c]  As  the  lining  of  the  ventricles,  which  is  the  direct  continuation 
of  the  gray  substance  of  the  spinal  cord. 

(d)  As  the  cerebellar  cortex,  an  expansion  covering  the  surface  of  the 
cerebellum.    Discrete  masses  also  occur  in  the  interior  of  the  cerebellum. 

All  these  aggregations  have  numerous  connections  with  one 
another  by  means  of  fiber-tracts. 

THE  CEREBRAL  CORTEX. 

In  vertical  sections  of  the  cerebral  cortex  four  zones,  not  sharply 
defined  from  one  another,  may  be  distinguished. 

i.  The  molecular  zone  (neuroglia  layer),  the  most  superficial,  in 
ordinary  preparations  appears  finely  granular  or  reticulated  and  contains, 
besides  many  glia-cells,  an  interlacement  of  medullated  nerve-fibers  run- 
ning horizontally,  the  tangential  fibers  (Fig.  101).  By  means  of  Golgi's 
method,  it  may  be  seen  that  the  reticulum  is  partly  formed  by  the  den- 
drites  of  the  pyramidal  cells  of  the  second  and  third  zones  and  partly 
by  the  processes  of  glia-cells.  Besides  the  latter,  the  cells  of  Cajal  occur 
in  the  molecular  zone  ;  they  possess  an  irregularly-shaped  cell-body  that 
sends  out  very  long  processes  running  parallel  to  the  surface,  from  one 
portion  of  which,  vertically  to  the  surface,  ascending  lateral  twigs  arise, 
while  one  or  more  processes  penetrate  into  the  depths  of  the  cortex* 
(Fig.  102,  i). 

*  In  animals  four  and  even  more  "  nerve-processes  "  of  Cajal's  cells  have  been  described  ; 
in  man  the  demonstration  of  nerve-processes  has  not  yet  been  accomplished.  The  nervous 
nature  of  Cajal's  cells  is  not  definitely  established  ;  I  am  strongly  inclined  to  regard  them  as 
glia-cells. 


Molecular 
layer. 


x 


Tangent  i; 
fibers. 


Superradial 
reticulum. 


Stripes  of  J     J 
Gennari.    1    i 


Layer  ol 
small  pyra- 
midal cells. 


Layer  of 
large   pyra- 
cells. 


*     ~~  *I  *  '       '  *'  I  -Sei 

-  A-    .  -    -     /    mldal 
t^v 

fe,/ 


Interradial     -- -ifjiB^ 
reticulum. 


Radial 
bundles 


Blood- 
vessels. 


Layer  of 
polymor- 
phous 
nerve-cells. 


Medulla. 


FIG.  ioi.— VKRTICAL  SECTION  OF  HUMAN  CEREBRAL  FIG    102.— SCHEME  OF  CEREBRAL  CORTEX,  sketched  from 


CORTEX.     X  60.    Techn.  No.  71. 


specimens  prepared  according  to  Techn.  No.  73,  b. 
i.  CellofCajal.  2,2'.  Small  pyramidal  cells.  3.  Large 
pyramidal  cell.  4.  Polymorphous  cell.  5,  5'.  Cells  of 
the  second  type.  6.  Nerve-fiber  ending  in  the  super- 
ficial zone:  a,  mossy-cell ;  b,  spider-cell  (glia-cells). 
The  ependymal-cells  are  not  represented. 


173 


174 


HISTOLOGY. 


2.  The  zone  of  the  small  pyramidal  cells  (Fig.  101,  102)  is  charac- 
terized by  ganglion-cells  from  10  to  12  fj.  in  size  and  of  a  pyramidal  form  ; 
the  apex  of  the  pyramidal  cell  is  prolonged  into  a  long  ramifying  proto- 
plasmic process  (dendrites),*  that  after  giving  off  minute  lateral  twigs 
enters  the  molecular  zone,  where  it  terminates  in  numerous,  often  serru- 
late, branches  (Fig.  102,  2);  smaller  dendrites  spring  from  the  lateral 
surfaces  and  from  the  inferior  surface  of  the  cell.  The  nerve-process 
always  arises  from  the  base  and  after  giving  off  branched  collateral 
fibers,  as  a  rule,  passes  toward  the  white  substance,  there  to  become 
the  axis-cylinder  of  one  or,  by  division,  of  two  nerve-fibers  ;  occasionally, 
however,  it  turns  and  runs  to  the  molecular  layer,  where  it  divides  and 
enters  the  web  formed  by  the  tangential  fibers 
(Fig.  102,  2').  The  nerve-processes  and  the 
collateral  fibers  are  enveloped  in  a  medullated 
sheath. 

3.  The  zone  of  the  large  pyramidal  cells  is 
distinguished  from  the    preceding  zone    by  the 
greater  size  of  its  elements  (from  20  to  30  //),  the 
extremely  robust  nerve-process,  after  giving  off 
in  the  gray  substance  several  collaterals  always 
goes  to  the  white  substance  (Fig.  102,  3). 

4.  In  the  zone  of  the  polymorphous  nerve  - 
cells  the  majority  of  the   elements  are  oval    or 
polygonal  ;    an   apical  dendrite  is   wanting,   the 
delicate  nerve-process,  after  sending  off  a  num- 
ber of  collaterals,    enters   the  white   substance, 
where    it   passes     into     one     or,    dividing     into 
T-branches,  into  two  nerve-fibers  (Fig.  102,  4). 

In  the  last  three  zones  ganglion-cells  of  the 
second   type    also  are    found.     Their    branched 

nerve-process  sometimes  is  confined  to  the  gray  matter  in  the  vicinity  of 
the  cell,  sometimes  extends  to  the  molecular  zone,  where  richly  branched 
it  terminates  (Fig.  102,  5,  5'). 

The  last  two  zones  contain  numerous  medullated  nerve-fibers. 
They  are  partly  arranged  in  thick  "  radiating  "  bundles,  which  resolve 
into  single  fibers  near  the  zone  of  the  small  pyramidal  cells  (Fig.  101). 
These  bundles  are  formed  by  the  descending  medullated  nerve-processes 


Nerve-process. 

FIG.  103. — PYRAMIDAL  CELL 
FROM  A  PERPENDICULAR  SEC- 
TION OF  THECERKBRAL  COR- 

TEX  OF  ADULT  MAN.  X  120. 
The  terminal  branches  of  the 
dendrites  running  toward  the 
molecular  layer  are  not  visi- 
ble. Techn.  No.  73  b. 


*  For  this  reason  it  is  difficult  to  determine  the  size  of  the  pyramidal  cells  ;  the  consid- 
erable differences  in  the  estimated  size  may  be  referred  to  this  gradual  passage  of  the  cell-body 
into  the  apical  process. 


THE    CENTRAL    NERVOUS    SYSTEM. 


175 


of  the  large  and  small  pyramidal  cells,  by  thick  medullated  nerve-fibers 
of  unknown  origin,  that  ascend  from  the  white  substance  toward  the 
cortex  (Fig.  102,  6),  where  they  repeatedly  divide  and  form  the  "super- 
radial  "  and  the  tangential  plexus  (Fig.  102),  and  finally  end  in  free 
branches.  Another  set  of  medullated  nerve-fibers  runs  transversely  to 
the  radiating  bundles  and  forms  the  interradial  reticulum  ;  this  is  some- 
what condensed  toward  the  "  superradial "  reticulum  and  thus  represents 
the  stripes  of  Gennari  or  Baillarger  (Fig.  101).  This  and  the  interradial 
reticulum  are  composed  of  the  medullated  collateral  fibers  of  the  nerve- 
processes  of  the  pyramidal  cells. 

The  structure  of  the  cerebral  cortex  is  modified  in  certain  localities. 
In  the  hippocampal  and  uncinate  convolutions  the  tangential  fibers  are 


Blood-vessel. 


Mossy-cell.  Spider-cell. 

FIG.  104. — FROM  SECTIONS  OF  THE  BRAIN  OF  ADULT  MAN.    X  280.    Techn.  No.  73  b. 

present  in  larger  numbers  and  form  an  expanded  net-like  white  layer, 
the  substantia  reticularis  alba.  In  the  vicinity  of  the  calcarine  fissure  the 
stripes  of  Gennari  are  developed  into  the  bundle  of  Vicq  d'  Azyr,  which 
may  be  seen  by  the  unaided  eye.  Greater*  or  lesser  deviations  occur  in 
many  localities,  which  render  a  classification  according  to  the  above  de- 
scription much  more  difficult. 

Finally,  extensions  of  the  pia  that  penetrate  in  company  with  the 
blood-vessels  participate  in  the  construction  of  the  cerebral  cortex,  as 
also  the  ncuroglia  ;  this  like  that  of  the  spinal  cord  consists  of  ependymal 
cells  and  r,f  astrocytes.  In  the  embryo  the  peripheral  processes  of  the 


*  Regarding  the  minute  structure  of  the   cortex  of  the  cornu  ammonis  and  the  bulbus 
olfactorius,  the  reader  is  referred  to  special  text-books. 


1 76  HISTOLOGY. 

former  extend  to  the  free  surface.  Of  the  latter  two  varieties  are  dis- 
tinguished. The  one  variety  are  characterized  by  their  small  cell-body 
and  long,  rigid,  little-branched  processes,  of  which  the  most  delicate  rest 
like  a  short  turf  on  the  cell-body  ;  they  are  called  spider-cells,  and  chiefly 
occur  in  the  white  substance.  The  other  variety,  the  mossy-cells,  have 
short,  gnarled,  richly-branched  processes  and  are  mainly  found  in  the 
gray  substance,  where  they  are  in  intimate  relation  with  the  blood- 
vessels, to  the  walls  of  which  they  are  often  attached  by  one  thicker 
process  (Fig.  104).  On  the  surface  of  the  cerebral  cortex  there  is  a  glia- 
zone  formed  by  the  ends  of  the  thitherward  extending  processes  of  the 
glia-cells. 

THE  CEREBRAL  GANGLIA. 

The  gray  substance  of  the  cerebral  or  basal  ganglia  consists  of 
ganglion-cells  varying  in  size,  medullated  nerve-fibers,  and  neuroglia. 
The  macroscopic  variations  in  color  depend  on  the  different  proportions 
in  which  the  ganglion-cells  and  nerve-fibers  are  mingled  :  wealth  of  gan- 
glion-cells is  rendered  perceptible  by  a  dark  red-brown  color,  profusion 
of  nerve-fibers  by  a  pale  yellow-gray  color. 

THE  GRAY  SUBSTANCE  OF  THE  VENTRICLES. 

The  gray  substance  of  the  ventricles  extends  from  the  floor  of  the 
fourth  ventricle  through  the  aqueduct  of  Sylvius  into  the  third  ventricle, 
to  the  tuber  cinereum  and  the  infundibulum.  It  is  of  especial  interest  as 
the  place  of  origin  of  the  cranial  nerves.  It  is  composed  of  neuroglia, 
nerve-fibers,  and  ganglion -cells  ;  the  majority  of  the  latter  are  multipolar 
and  in  certain  localities  are  distinguished  by  their  size  (in  the  nucleus  of 
the  hypoglossal  nerve),  or  by  their  peculiar  form  (the  spherical  ganglion- 
cells  in  the  upper  pair  of  the  corpora  quadrigemina). 

An  extension  of  the  neuroglia  and  ependyma  lining  the  central 
canal  of  the  spinal  cord  lines  the  floor  of  the  fourth  ventricle,  the  aque- 
duct of  Sylvius  (aquaeductus  cerebri),  the  inner  surface  of  the  third  and 
the  lateral  ventricles  ;  it  is  composed  of  similar  elements.  The  columnar 
or  cubical  cells  of  the  ependyma  of  the  ventricles  in  the  newborn,  and  in 
part  also  in  the  adult,  possess  cilia. 

THE  CEREBELLAR  CORTEX. 

The  cerebellar  cortex  consists  of  three  well-defined  strata  of  gray 
substance,  of  which  the  outer  and  the  inner  are  macroscopically,  the 
middle,  on  the  contrary,  only  microscopically  perceptible  :  they  are  from 
within  outward,  the  granule  layer,  the  ganglionic  layer,  and  the  molecular 
layer. 


THE    CENTRAL    NERVOUS    SYSTEM. 


177 


Gray 
layer. 


Cortex. 


The  granule  layer,  the  innermost,  is  characterized  by  its  rust  color 
and  consists  of  numerous  strata  of  small  cells,  that  by  the  ordinary 
methods  exhibit  a  proportionately 
large  nucleus  and  a  very  small 
amount  of  protoplasm.  By  the 
aid  of  Golgi's  method  it  becomes 
apparent  that,  apart  from  the  glia- 
cells,  two  varieties  of  ganglion-cells 
are  present :  small  granule -cells  and 
large  granule-cells.  The  former 
are  multipolar  ganglion-cells  with 
short  dendrites  with  claw-like  end- 
ings and  a  delicate  nonmedullated 
nerve-process,  that  passes  vertically 
into  the  molecular  layer  and  there 
divides  into  two  T-branches  that  run  parallel  to  the  surface  and  to  the 
axis  of  the  convolution  and  terminate  in  free  unbranched  ends  (Fig.  106 


Medulla.' 


FIG.  105.— FROM  A  PERPENDICULAR  SECTION 
THROUGH  THE  CORTEX  OF  THE  CEREBELLUM  OF 
ADULT  MAN.  X  50.  Techn.  No.  72. 


FIG.   106.  —  SMALL    GRANULE- 
CELL  WITH   A   PIECE  OF  THE 

NERVE-PROCESS,  N,  AND 
SHORT  DENDRITES,  D.  From 
a  section  through  the  cortex 
of  the  cerebellum  of  a  six- 
week-old  cat.  X4QO.  Techn. 
No.  74. 

12 


Nerve- 
process. 


Nerve-plexus. 


FIG.  107.— LARGE  GRANULE-CELL  FROM  A  SECTION  THROUGH  THH 
CORTEX  OF  THE  CEREBELLUM  OF  A  SIX-WEEK-OLD  CAT.  X  200. 
Techn.  No.  74. 


HISTOLOGY. 

and  109,  i).  The  small-granule-cells  form  the  chief  mass  of  the  cellular 
elements  of  the  granule-layer.  Less  numerous  are  the  large  granule- 
cells,  multipolar  ganglion-cells  more  than  twice  the  size  of  the  smaller 
elements,  the  ramifying  dendrites  of  which  extend  into  the  outermost 
gray  layer,  the  nerve-process  of  which,  running  in  the  opposite  direction, 
rapidly  divides  and  terminates  in  a  rich  ramification  penetrating  the 
entire  granule-layer  (Fig.  107  and  109,  2). 

A  dense  plexus   of  medullated  nerve-fibers  occurs  in  the  granule- 


Dendrites 


Cell-body. 


^ Axis-cylinder  process. 


FIG.  1 08.— NERVE-CELL  (CELL  OF  PURKINJE)  FROM  A  SECTION  THROUGH  THE  HUMAN  CEREBELLAR 
CORTEX.     X  180.    Techn.  No.  74. 


layer  (Fig.  109,  3)  ;  the  greater  part  of  the  fibers  come  from  the  white 
substance  of  the  cerebellum  and  at  the  boundary  between  the  granule 
and  the  ganglionic  layer  form  a  horizontal  bundle  (3')  running  transverse 
to  the  longitudinal  axis  of  the  convolution,  from  which  fibers  ascend  into 
the  molecular  layer  (3").  A  small  portion  of  this  plexus  is  formed  by 
the  medullated  nerve-processes  of  the  cells  of  Purkinje. 

The  middle  ganglionic  stratum  of  the  cerebellar  cortex  consists  of  a 


THE    CENTRAL    NERVOUS    SYSTEM. 


179 


simple  layer  of  very  large  multipolar  ganglion-cells,  the  cells  of  Purkinjc. 
Their  somewhat  pear-shaped  bodies  send  two  robust  dendrites  into  the 
molecular  layer,  where  they  terminate  in  an  uncommonly  rich  arboriza- 
tion and  extend  to  the  free  surface  (Fig.  109,  4).  The  ramification  does 
not  extend  in  all  directions,  but  only  in  planes  transverse  to  the  long  axis 
of  the  convolution,  therefore,  the  entire  ramification  can  be  seen  only  in 
transverse  sections  of  the  convolution.  From  the  opposite  pole  of  the 


•     -  .  •  .  •       .    '•  -'  •-    .".     •'  r 

i:  :':•:•  ^~-^^^hSol 

'.'•'•'.  '.'.'.  ••:'•  '•'  :''••'•'•   S*oSJo°C°oO^ 
"•*'"«     ••  ••'        ^OrTilOO  o  o  C' 


Molecular  layer. 


Granule-layer.        Medulla. 


FIG.  109.— SCHEME  OF  THE  CEREBELLAR  CORTEX,  sketched  from  specimens  prepared  according  to 
Techn.  No.  74.  i.  Small  granule-cells ;  2,  large  granule-cells;  3,  plexus  of  nerve-fibers;  3',  hori- 
zontal bundles  ;  3",  fibers  of  the  molecular  layer ;  4,  cell  of  Purkinje  ;  5,  basket-cell ;  6,  small  cortical 
cells,  a,  Glia-cells  of  the  molecular  layer;  d,  mossy-cell  resembling  a  glia-cell ;  c,  spider-cell. 

cell  the  nerve-process  arises,  that  immediately  acquires  a  medullated 
sheath  and  passing  through  the  granule-layer  enters  the  white  substance 
of  the  cerebellum  ;  while  still  within  the  granule-layer  it  sends  off  colla- 
terals that  branch  there  and,  in  part,  run  back  between  the  cells  of  Pur- 
kinje (Fig.  109). 

The  outermost  gray  or  molecular  layer  is  distinguished  by  its  gray 
color   and   contains  multipolar   ganglion-cells,   the    dendrites   of  which 


i8o 


HISTOLOGY. 


mainly  extend  toward  the  surface.  Their  long  nerve-process  runs  hori- 
zontally in  the  transverse  axis  of  the  convolution,  sends  toward  the  sur- 
face a  few  collaterals,  toward  the  interior  gives  off  at  successive  intervals 
delicate  branches  the  terminal  ramifications  of  which  form  a  basket-like 
network — fiber-basket — around  the  bodies  of  Purkinje's  cells  (Fig.  109, 
5,  and  Fig.  no).  The  "basket"  often  also  embraces  the  beginning  of 
the  axis-cylinder  process  of  Purkinje's  cell.  These  cells  are  called 
basket-cells.  * 

The  medullated  nerve-fibers  in  the  molecular  layer  are  extensions 
of  the  reticulum  of  the  granule-layer  and  in  part  pass  toward  the  surface, 
where  after  losing  the  medullary  sheath  they  terminate  in  free  branches 


Embryonal  su- 
perficial gran- 
ule-laver. 


Part  of  the  , 

granule-layer.   ' 


Dendrites.      Nerve-process. 


Cells  of  Purkinje. 


FIG.  i io.— BASKET-CELL,  FROM  A  SECTION  THROUGH  THE  CEREBELLAR  CORTEX  OF  A  SIX-WEEK-OLD 
CAT.  X  240.  The  five  cells  of  Purkinje  were  not  blackened  but  were  plainly  visible;  only  the  out- 
lines of  their  bodies  are  sketched.  Techn.  No.  74. 


between  the  arborizations  of  the  protoplasmic  processes  of  the  cells  of 
Purkinje,  in  part  they  run  horizontally  between  the  bodies  of  these  cells, 
parallel  to  the  axis  of  the  convolution. 

The  neuroglia  of  the  cerebellum  consists  of  two  kinds  of  cells  :  (i)  the 
one  kind  lie  at  the  outer  boundary  of  the  granule-layer  ;  they  have  a 
small  cell-body  that  sends  a  few  short  processes  to  the  interior,  but 
many  long  processes  in  a  straight  course  toward  the  free  surface,  where 
they  terminate  in  a  triangular  expansion  (Fig.  112,  left).  In  this  way  a 
relatively  thick  peripheral  glia-layer  is  formed.  (2)  The  other  kind  are 


*  The  so-called  small  cortical  cells  (Fig.  109  and  Fig.  Ill)   are    also  basket-cells,  the 
processes  of  which  have  "  blackened  "  for  a  shorter  distance. 


THE    CENTRAL    NERVOUS    SYSTEM. 


181 


stellate  cells  resembling  the  mossy-cells  of  the  cerebral  cortex  (Fig.  1 12, 
right) ;  they  occur  in  all  the  strata.  In  the  white  substance  typical 
spider-cells  are  found. 

So  long  as  the  cerebellar  cortex  is  not  fully  developed  it  is  charac- 
terized by  a  series  of  peculiarities  that  are  wanting  in  the  adult.  In 
embryos  and  young  animals  there  is  over  the  as  yet  slightly-developed 
molecular  layer  a  superficial  granule-stratum  ;  the  structures  in  the 


Small  cortical  -^  -~ 
cells. 


•     Ascending 
^i  nerve-fiber. 


Small  granule-cells. 


Glia-cell. 


FIG.  in. — FROM  A  SECTION  OF  THE  CEREBELLAR  CORTEX  OF  ADULT 
MAN.  X  240.  The  transverse  lines  are  nerve-processes  of  basket- 
cells.  The  cell  of  Purkinje  and  the  glia-cell  were  sketched  in  out- 
line from  another  part  of  the  specimen  for  the  purpose  of  demonstrat- 
ing the  difference  in  size.  Techn.  No.  74. 


FIG.  112.  —  Two  GLIA-CELLS 
FROM  A  SECTION  THROUGH 
THE  CEREBELLAR  CORTEX  OF 
ADULT  MAN.  X  90.  On  the 
right  the  body,  />,  and  the 
dendrites,  I",  of  a  cell  of 
Purkinje  are  sketched  in  out- 
line to  demonstrate  the  differ- 
ence between  this  element  and 
the  glia-cells.  Techn.  No.  74. 


granule-layer  described  under  the  name  of  "mossy-fibers"  are  develop- 
mental forms  of  medullated  nerve-fibers  ;  of  like  significance  are  the 
"  climbing  plexuses,"  which  are  found  in  the  environs  of  the  ramifying 
protoplasmic  processes  of  the  cells  of  Purkinje. 

The  union  of  the  elements  of  the  cerebellum,  as  everywhere  in  the 
central  nervous  system,  is  only  by  contact,  not  by  direct  connection. 

The    white  substance,  the   medulla,  of    the    cerebrum   and   of  the 


182 


HISTOLOGY. 


cerebellum,  apart  from  the  elements  of  the  supporting  framework  (con- 
nective tissue  and  neuroglia),  consists  throughout  of  medullated  nerve- 
fibers  without  a  neurilemma  and  varying  in  thickness  from  2.5  to  7  p. 

The  hypophysis  cerebri  (pituitary  body)  is  composed  of  two  genetic- 
ally different  parts  :  (i)  a  posterior  small  lobe  that  belongs  to  the  brain 
and  is  a  continuation  of  the  infundibulum  ;  it  contains  delicate,  much- 
branched  nerve-fibers,  that  form  a  very  compact  plexus,  and  connective 
tissue,  many  blood-vessels,  and  cells  that  closely  resemble  bipolar  or 
multipolar  ganglion-cells,  but  the  nature  of  which  is  still  uncertain  ;  (2) 
an  anterior  larger  lobe  derived  from  a  diverticulum  of  the  embryonal  oral 
cavity ;  it  contains  gland  follicles  embedded  in  loose  vascular  connective 
tissue,  the  majority  of  which  are  solid  and  filled  with  clear  or  granular 


Anterior  lobe.  x 


Posterior  lobe. 


Hollow  gland- 
tubule. 


Blood-vessel  con- 
taining blood- 
corpuscles. 


Colloid  "  sub- 
stance. 


Multipolar  cell. 


Connective-tissue 
fibers. 


FIG.  113.— PORTION  OF  A  HORIZONTAL  SECTION  OF  A  HUMAN  PITUITARY  BODY,  showing  the  boundary- 
line  between  the  anterior  and  posterior  lobe.  Two  gland-tubules  on  the  left  contain  each  a  granular 
epithelial-cell.  X  220.  Techn.  No.  75. 


cubical  epithelial-cells  (Fig.  113).  Only  a  few  of  the  follicles  toward  the 
border  of  the  smaller  lobe  are  hollow  and  occasionally  contain  a  mass 
resembling  the  colloid  substance  of  the  thyroid  body. 

The  pineal  body  (epiphysis,  corpus  pineale)  is  derived  from  a  fold  of 
the  wall  of  the  primitive  brain-vesicle  and  consists  of  epithelial-cells,  some 
of  which  have  delicate  processes,  and  of  a  connective-tissue  envelope 
from  which  septa  extend  into  the  interior  of  the  organ.  Almost 
invariably  "brain-sand"  (acervulus  cerebri)  is  found  in  the  epiphysis, 
rounded  concretions  from  5  Mo  I  mm.  in  size,  with  an  uneven,  mulberry- 
like  surface  (Fig.  114).  They  are  composed  of  an  organic  basis  and 
calcium  carbonate  and  magnesium  phosphate. 

Not  infrequently  (especially  in  advanced   life)  there  occur  in  the 


THE    CENTRAL    NERVOUS    SYSTEM. 


183 


brain-substance  round  or  discoid  bodies  exhibiting  distinct  concentric 
stratifiati on,  which  stain  violet  on  treatment  with  iodin  and  sulphuric  acid, 
therefore  are  related  to  amylum  (Fig.  115,  a).  These  corpuscula  ainy- 


FlG.  114.— ACERVULUSCEREBRI  FROM  THE  PlXEAL 

BODY  OF  A  WOMAN  SEVENTY  YEARS  OLD.    X  50. 
Techn.  No.  76. 


FIG.  115.— FROM  A  TEASED  PREPARATION  OF  GRAY 
SUBSTANCE  FROM  THE  WALL  OF  A  VENTRICLE  OF 
THE  HUMAN  BRAIN.  X  240.  a,  Corpuscula  atny- 
lacea ;  b,  myelin  drops;  c,  red  blood-corpuscles; 
rf,  ependymal  cells  ;  <?,  medullated  nerve-fibers  ; 
/,  ganglion-cell.  Techn.  No.  77. 


lacea,  almost  constant  within  the  walls  of  the  ventricles  of  the  brain, 
are  present  in  many  other  localities,  as  well  in  the  gray  as  in  the 
white  substance. 


THE  MEMBRANES  OF  THE  CENTRAL  NERVOUS  SYSTEM. 

Two  connective-tissue  membranes  envelop  the  brain  and  the  spinal 
cord  :  the  dura  and  pia. 

The  dura  of  the  spinal  cord  (dura  mater  spinalis)  consists  of  compact 
fibrous  connective  tissue  and  numerous  elastic  fibers,  flat  connective-tissue 
cells  and  plasma-cells  (p.  79  and  Fig.  120).  The  inner  surface  is  covered 
by  a  simple  layer  of  flat  epithelial-cells  (endothelium).  It  is  poor  in 
nerves  and  blood-vessels. 

The  dura  of  the  brain  (dura  mater  cerebralis)  is  at  the  same  time 
the  periosteum  of  the  inner  surface  of  the  cranium  and  consists  of  two 
lamellae  :  (i)  an  inner,  which  corresponds  to  the  dura  of  the  cord  and  is 
of  like  structure,  and  (2)  an  outer,  which  corresponds  to  the  periosteum 
of  the  vertebral  canal.  It  is  composed  of  the  same  elements  as  the  inner 
lamella,  with  the  exception  that  the  outer  fiber-bundles  are  disposed  in  a 
different  direction;  anteriorly  and  laterally  they  extend  posteriorly  and 
medianward,  like  the  inner  fibers,  which  run  from  the  anterior  median 
region  posteriorly  and  lateralward.  The  outer  lamella  is  rich  in  blood- 
vessels, which  pass  from  it  into  the  cranial  bones. 

The  pia  of  the  brain  and  the  spinal  cord  is  a  two-layered  sack.  The 
outer  layer,  the  arachnoid  of  authors,  is  covered  on  its  free  surface  by  a 


or  THC 
UNIVERSITY 


184  HISTOLOGY. 

simple  layer  of  epithelium  (endothelium),  and  is  not  closely  attached  to  the 
dura.  The  inner  layer  (the  "  pia  ")  closely  invests  the  surface  of  the  brain 
and  the  spinal  cord  and  sends  vascular  processes  into  their  substance. 
The  arachnoid  and  the  pia  are  joined  together  by  numerous  lamellae  and 
trabeculae  extending  from  the  inner  surface  of  the  former  to  the  outer 
surface  of  the  latter.  Hernia-like  evaginations  occur  on  the  outer  surface 
of  the  arachnoid  in  certain  localities,  in  particular  near  the  superior  longi- 
tudinal sinus,  which  pushing  the  attenuated  dura  before  them  project 
into  the  venous  sinus.  These  are  the  so-called  arachnoidal  granulations 
(Pacckioni\  which  were  long  regarded  as  pathologic.  The  pia  is  com- 
posed of  delicate  connective-tissue  bundles  and  plate-like  cells,  which 
cover  the  inner  surface  of  the  arachnoid  and  the  lamellae  and  trabeculse. 

Blood-vessels.  x  Epithelium. 


FIG.  116. — PORTION  OF  THE  PLEXUS  CHOROIDEUS  OF  ADULT  MAN.  X  80.  x,  Blood-vessel  in  optical 
cross-section.  The  dots  in  the  epithelium  are  not  nuclei,  but  pigment  and  iat-granules.  Techn. 
No.  78  b. 

The  telce  choroidecz  and  plexus  choroidei  consist  of  connective  tissue 
and  numerous  blood-vessels,  the  fine  ramifications  of  which  are  united 
into  lobules  that  are  suspended  within  the  ventricles.  They  are  covered 
by  a  simple  layer  of  cubical  epithelial -cells,  ciliated  in  the  newborn,  which 
enclose  pigment-granules  or  oil-globules. 

THE  VESSELS  OF  THE  CENTRAL  NERVOUS  SYSTEM. 
The  blood-vessels  of  the  central  nervous  system  form  a  narrow- 
meshed  capillary  network  in  the  gray,  a  wide-meshed  network  in  the 
white  substance,  which  are  everywhere  connected  with  each  other.  The 
capillaries  of  the  cerebral  cortex  open  into  veins  that  do  not  take  their 
origin  in  the  cortex,  but  beneath  in  the  white  substance  and  from  there 

o 

traverse  the  cortex  and  go  to  the  veins  lying  in  the  pia.  Therefore  the 
blood  in  the  capillaries  must  traverse  the  entire  cortex  before  it  empties 
into  the  veins.  All  the  blood-vessels  possess  a  second  so-called  adven- 
titial  sheath,  which  often  consists  of  only  a  simple  stratum  of  endothelial 


THE    PERIPHERAL    NERVOUS    SYSTEM.  185 

cells.  The  walls  of  the  intradural  venous  sinuses  are  formed  by  a 
simple  endothelial  membrane. 

The  Lymph-channels. — Between  the  dura  and  the  arachnoid  there 
is  a  deep  capillary  cleft  or  fissure,  the  subdural  space,  which  communi- 
cates with  the  deep  cervical  lymph-vessels  and  lymph-nodes  (at  least  in 
the  rabbit  and  the  dog),  with  the  lymph-channels  of  the  peripheral  nerves, 
with  the  lymph-vessels  of  the  nasal  mucous  membrane,  with  the  smaller 
clefts  (juice-canals)  in  the  dura,  and  finally,  round  the  arachnoidal  villi, 
with  the  intradural  venous  sinuses.  The  fluid  in  the  subdural  space  is 
very  scanty. 

The  subaraclmoidal  space,  that  between  the  two  layers  of  the  pia 
(or  arachnoid  and  pia),  communicates  with  the  "juice-channels  "  of  the 
peripheral  nerves,  the  lymph-vessels  of  the  nasal  mucous  membrane,  the 
interior  of  the  ventricles  of  the  brain  and  of  the  central  canal  of  the  spinal 
cord.  The  fluid  in  the  subarachnoid  space  is  very  abundant ;  it  is  called 
the  cerebro-spinal  fluid. 

The  spaces  occurring  within  the  adventitial  sheath  of  the  blood- 
vessels can  be  injected  from  the  subarachnoidal  space.  They  are  called 
adventitial  lymph-spaces. 

The  spaces  filled  only  by  injecting  the  brain-substance  itself  cannot 
be  included  in  the  system  of  lymphatic  channels.  These  spaces  occur  as 
pericelhdar  spaces  surrounding  the  larger  ganglion-cells  of  the  cerebral 
cortex,  also  many  glia-cells  ;  as  perivascidar  spaces  of  the  blood-vessels, 
that  formed  by  the  adventitial  sheath  excepted  ;  and  between  the  pia  and 
the  cerebrum,  as  the  epicerebral  space.  These  may  be  regarded  as  an 
independent  juice-canal  system. 


2.   THE  PERIPHERAL   NERVOUS  SYSTEM. 
THE  NERVES. 

4 

The  cerebro-spinal  nerve -trunks  chiefly  consist  of  medu  Hated  nerve- 
fibers  varying  in  thickness  and  of  only  a  few  gray  nerve-fibers  ;  therefore 
by  reflected  light  they  appear  white.  Their  mode  of  union  agrees  in 
many  respects  with  that  of  the  striated  muscle-fibers.  A  sheath  formed 
of  loose  connective  tissue  and  elastic  fibers,  often  containing  clusters  of 
fat-cells,  surrounds  the  entire  nerve.  It  is  called  the  epineurium  (Fig. 
117).  Extensions  of  the  epineurium  in  the  interior  of  the  nerve  sur- 
round the  (so-called  secondary)  nerve-fiber  bundles  (funiculi),  of  which 
each  is  enveloped  by  the  concentrically-lamellated  connective-tissue 
pcrincurium.  From  the  latter  connective-tissue  septa  extend  into  the 


1 86 


HISTOLOGY. 


interior  of  the  secondary  nerve-fiber  bundles  ;  they  constitute  the  endo- 
neurium.  Finally,  delicate  lamellae  from  the  endoneurium,  the  fiber 
sheaths,  corresponding  to  the  perimysium  of  the  single  muscle-fiber, 
surround  each  individual  nerve-fiber.  These  sheaths  are  in  direct  con- 


Fat-cells. 


Artery    in     transverse 
section. 


Cross-section    of    bun-  Z 
dies  of  nerve-fibers. 


Epineurium. 


Perineurium. 


Endoneurium. 


FIG.  117.— PORTION  OF  CROSS-SECTION  OF  HUMAN  MEDIAN  NERVE.     X  20.    Techn.  No.  79. 

nection  with  processes  of  the  dura  and  the  pia.  Perineurium  and 
endoneurium  are  composed  of  bundles  of  fibro-elastic  tissue  and  of  a 
number  of  concentric  lamellae ;  each  lamella  is  formed  by  a  simple  layer 
of  flattened  connective-tissue  cells,  the  outlines  of  which  can  be  demon- 


Blood-vessel 
containing 
blood-cor- 
puscles. 


Axis-cylinder. 

Medullary 

sheath. 


Perineu- 
rium. 


Endo- 
neurium. 


Fibrillar  sheath. 


FIG.  118. — PORTION  OF  CROSS-SECTION  OF  HUMAN  MEDIAN  NERVE.     X  220.    Techn.  No.  79. 


strated  by  silver  staining.  The  fiber-sheaths,  in  addition  to  delicate 
connective-tissue  bundles,  also  consist  of  plate-like  cells.  The  nerve- 
fiber  bundle  not  infrequently  divides  ;  a  variable  number  of  nerve-fibers 
branch  off  from  one  funiculus  to  join  another  funiculus,  the  result  of 


THE    PERIPHERAL    NERVOUS    SYSTEM.  l8/ 

which  is  a  narrow-angled  plexus  of  nerve-fiber  bundles.  Division  of  the 
nerve-fibers  does  not  occur  until  at  the  periphery: 

The  sympathetic  nerve-tnmks  are  partly  whiter  and  partly  grayer  in 
color,  depending  upon  the  greater  or  lesser  number  of  fine  medullated 
nerve-fibers  present ;  for  example,  the  splanchnic  nerves  contain  many 
medullated  nerve-fibers,  while  the  gray  branches  of  the  abdominal  and 
pelvic  plexuses  contain  only  a  very  few  of  the  thinnest  medullated  and, 
on  the  other  hand,  numerous  nonmedullated  nerve-fibers.  One  portion 
of  the  medullated  nerve-fibers  are  continuations  of  the  spinal  nerves,  an- 
other portion  are  nerve-processes  of  sympathetic  nerve-cells  ;  long  den- 
drites  of  sympathetic  nerve-cells  occasionally  occur  in  the  course  of  the 
sympathetic  nerves.  The  nerve-fibers  are  held  together  and  grouped 
into  bundles  by  connective  tissue. 

The  blood-vessels  run  lengthwise  within  the  epineurium  and  form 
capillary  networks  with  elongated  meshes  that  are  supported  by  the 
perineurium  and  endoneurium. 

The  lymph-channels  occur  in  the  capillary  clefts  between  the  lam- 
ellae of  the  perineurium  and  between  the  individual  nerve-fibers,  so  that 
each  nerve-fiber  is  bathed  in  lymph.  They  are  in  communication  with 
the  subdural  and  the  subarachnoidal  space,  but  not  with  the  lymph- 
vessels  accompanying  the  nerve -trunk. 

THE  GANGLIA. 

Ganglia  are  groups  of  nerve-cells  intercalated  in  the  course  of  the 
peripheral  nerves.  They  are  usually  macroscopically  visible.  All  gan- 
glia consist  of  small  bundles  of  nerve-fibers  between  which  lie  ganglion- 
cells  partly  arranged  in  rounded  groups,  partly  in  longitudinal  rows  (Fig. 
119).  A  connective-tissue  capsule,  an  extension  of  the  perineurium, 
covers  the  outer  surface  of  the  ganglion  and  sends  into  the  interior  deli- 
cate processes  for  the  support  of  the  nerve-fibers  and  ganglion-cells.  The 
ganglia  are  very  rich  in  blood-vessels,  the  capillaries  of  which  surround 
the  individual  cells.  Respecting  the  minute  structure,  differences  exist 
between  the  spinal  ganglia  and  the  sympathetic  ganglia. 

The  cells  of  the  spinal  ganglia  are  bipolar  in  the  embryo  ;  the 
processes  spring  from  opposite  poles  of  the  cell.  In  the  course  of  devel- 
opment the  two  processes  gradually  approach  each  other  by  attenuation 
of  the  portion  of  the  cell-body  from  which  they  arise,  until  finally  they 
proceed  from  a  common  stalk  ;  the  cell  thus  becomes  unipolar.* 


*  In  amphibians  and  birds,  also  in  the  embryos  of  mammals,  isolated  multipolar  ganglion- 
cells  occur;  but  their  dendrites  are  short  and  only  slightly  branched. 


188 


HISTOLOGY. 


The  process  of  the  adult  cell  receives  a  medullary  sheath  and  a 
neurilemma  very  near  to  its  exit  from  the  cell,  and  after  a  short  course 
invariably  divides  at  a  node  of  Ranvier  into  two  T-  or  Y-branches.  One 
branch,  the  cellulipetal,  passes  as  the  axis-cylinder  of  a  sensory  nerve- 
fiber  to  the  periphery  of  the  body  ;  the  other,  the  cellulifugal,  usually 
the  smaller  branch,  enters  the  spinal  cord  as  a  constituent  of  a  posterior 
nerve-root  and  terminates  in  free  branches  in  the  gray  substance.  Thus 
each  spinal  ganglion-cell,  by  its  undivided  process,  is  in  a  measure  inter- 
calated in  the  course  of  a  sensory  nerve-fiber.  The  cells  of  the  spinal 
ganglia  are  large,  round,  often  pigmented,  their  vesicular  nucleus  con- 
tains a  conspicuous  nucleolus.  Each  cell  is  enveloped  in  a  nucleated 

Nerve-cells. 


':.£."&*&• 


Nerve-fiber 
bundle. 


Nerve-fiber  bundle. 


Connective  tissue. 


FIG.  119.— LONGITUDINAL  SECTION  OF  THE  SPINAL  GANGLION  OF  A  CALF.     X  20.     (Scbaper.j 

Tech n.  No.  80. 


capsule  (Fig.  120)  which  consists  of  concentric  strata  of  flattened  con- 
nective-tissue cells  and  is  prolonged  on  to  the  process  of  the  cell  as  the 
fiber-sheath*  Gray  nerve-fibers  from  the  sympathetic  ganglia  occur  in 
the  spinal  ganglia,  which  branch  and  form  a  plexus  within  the  connective- 
tissue  capsule  of  the  spinal  ganglion-cells. 

Other  ganglia  possessing  the  same  structure  as  the  spinal  ganglia 
are  :     The  Gasserian,  the   jugular   ganglia,    the   plexus  nodosus   of  the 


*  Whether  any  nerve-fibers  pass  through  the  spinal  ganglia  that  do  not  enter  into  relation 
with  the  ganglion-cells  is  uncertain.  In  young  embryo  chicks  such  fibers  have  been  seen  coming 
from  the  cells  of  the  anterior  horns,  but  they  have  not  been  found  in  mammals. 


THE    PERIPHERAL    NERVOUS    SYSTEM. 


189 


vagus,  the  petrosal  and  the  geniculate  ganglia  ;  the  ganglia  of  the  audi- 
tory nerve  (ganglia  nervi  cochleae  et  nervi  vestibuli)  contain  bipolar  cells. 


Protoplasm.    - 


Nucleus. 


Nucleolus. 


Nucleated  sheath. 


Bundles  of  cross-sec- 
tioned nerve-fibers. 


>  O    '        &      £:' 

V 
:^r 


Nucleated  sheath  seen 
from  the  surface. 


Plasma-cells. 


Dura. 

FIG.  120. — FROM  A  CROSS-SECTION  OF  THE  GASSERIAN  GANGLION  OF  MAN.  X  240.  The  cell-processes 
cannot  be  seen  in  such  sections.  At  X  the  protoplasm  of  the  ganglion-cell  has  retracted  and  simu- 
lates a  process.  In  the  axis  of  the  transversely  cut  nerve-fibers  the  axis-cylinders  are  seen  in 
section.  Techn.  No.  80. 

The  sympathetic  ganglia  consist  of  nerve-fibers  and  of  small,  often 
pigmented  cells,  likewise  surrounded   by  a  nucleated  connective-tissue 


Artery  in  transverse 
section. 


Ganglion-cell 


Nucleated  sheath. 


iX_  -     Nucleated  sheath 
(from  the  surface). 


in 

cross-sec- 
tion. 


FIG.  121. — PORTION  OF  A  SECTION  OF  THE  SUPERIOR  CERVICAL  GANGLION  OF  MAN.     X  240. 

Techn.  No.  81. 

capsule,  that  possess  one  or  two  nuclei  (two  in  the  rabbit  and  the  guinea- 
pig).    The  cells  are  multipolar  ;  *  their  branched  dendrites  press  between 


*The  nerve-cells  of  the  sympathetic  ganglia  of  fishes  are  bipolar;  in  amphibians,  per- 
haps also  in  mammals,  ganglion-cells  occur,  of  which  the  single  process  with  T-branches  is 
embraced  by  a  ''spiral  fiber,"  that  surrounds  the  ganglion-cell  in  a  ramification  of  free  branches, 
similar  to  the  cells  of  the  spinal  ganglia. 


190  HISTOLOGY. 

the  neighboring  nerve-cells  through  to  the  periphery  of  the  ganglion, 
where  they  form  a  "  universal  *  peripheral  plexus  ;"  other  dendrites  even 
extend  into  the  neighboring  ganglia,  where  they  terminate  in  like  manner. 
Their  nerve-process  passes  directly  into  a  delicate  nerve-fiber,  that  either 
becomes  medullated  in  varying  length  or  remains  non-medullated.  These 
fibers  are  for  the  greater  part  motor  and  terminate — often  after  running 
an  extended  course — on  smooth  muscle-fibers  (p.  196) ;  one  portion  ter- 
minates in  free  endings  in  the  mucous  membrane  ;  the  terminal  ramifica- 
tions of  another  portion  surround  the  nerve-cells.  The  dense  terminal 
ramifications  of  the  medullated  nerve-fibers  coming  from  the  motor  spinal 
nerves  form  plexuses  which  in  part  lie  between  the  nerve-cells  and  in  part 
pierce  their  connective-tissue  capsules  and  surround  the  cells  themselves. 
To  the  sympathetic  ganglia  belong  the  ganglion  ciliaire,  sphenopal- 
atinum,  oticum,  and  submaxillaire. 


THE  PERIPHERAL  NERVE-ENDINGS. 

TERMINATIONS  OF  SENSORY  NERVES. 

The  peripheral  terminal  branches  of  the  sensory  nerves  either  are 
distributed  naked,  as  free  endings,  or  they  are  enclosed  by  epithelial  or 
connective-tissue  cells  with  which  they  form  special  endings  (terminal 
corpuscles,  end-organs). f 

The  free  nerve-endings  occur  in  such  a  manner  that  the  nerve-fiber 
loses  its  medullated  sheath,  divides  repeatedly  and  forms  a  plexus  of 
primitive  fibrils  that  terminate  in  pointed  or  club-shaped  ends.  These 
endings  chiefly  occur  in  stratified  epithelium.  They  have  been  demon- 
strated with  certainty  in  the  cornea,  in  the  oral  mucous  membrane  (see 
The  Taste-buds),  and  in  the  deeper  strata  of  the  epidermis.  In  the  latter 
cells  provided  with  long,  branched  processes,  the  cells  of  Langcrlians, 
occur ;  these  were  formerly  regarded  as  migrated  wandering  cells  from 
the  corium  and  it  is  possible  that  a  few  of  them  may  have  such  an  origin  ; 
but  the  majority  are  derived  from  ordinary  epithelial-cells  ;  all  the  tran- 
sitional forms,  from  the  typical  epithelial-cells  to  the  stellate  bodies  in 
question,  may  be  found. 

Sensory  nerves  have  been  found  also  in  the  muscles.  The  nerve- 
fibers  lose  their  medullated  sheath  and  invested  only  by  the  nerve-nuclei 


*The  expression  "  universal  "  is  used  in  contradistinction  to  the  statement  of  R.  y  Cajal, 
according  to  which  each  individual  nerve-cell  is  surrounded  by  a  basket  formed  of  dendrites. 

•f-The  nerve-endings  of  the  nenro-epithelial  cells  are  described  in  the  chapters  on  the 
special-sense  organs. 


THE    PERIPHERAL    NERVOUS    SYSTEM. 


divide  dichotomously  into  numerous  delicate  fibrillae  that  extend  length- 
wise between  the  muscle-fibers  and  terminate  in  free  endings. 

The  terminal  corpuscles  or  special  endings  may  be  divided  into  two 


I  Stratum  corneum. 
/  Stralum  lucidum. 


V  .; 


\  Stratum  germinati- 
vum. 


Epidermis. 


FIG.  122. — VERTICAL  SECTION  OF  THE  SKIN  OF  THE  GREAT  TOE  OF  A  MAN  TWENTY-FIVE  YEARS  OF 
AGE.  X  200.  The  cell-nuclei  of  the  stratum  germinativum  are  distinct  only  in  the  deepest  layer. 
/,  Cells  of  Langerhans  ;  »,  intra-epithelial  nerve-fibers.  P,  /*,  two  papillae  of  the  corium  ;  /'contains 
a  capillary  loop,  c,  of  which  only  one  limb  is  visible ;  F*  contains  a  tactile  corpuscle,  t,  with  two  ap- 
proaching medullated  nerve-fibers,  m.  Both  papillae  contain  nonmedullated  nerve-fibers.  Techn. 
No.  82. 

groups  :  tactile  cells  and  end-bulbs.  In  the  tactile  cells  the  nerve-fiber 
terminates  in  relation  with  one  or  two  cells  ;  in  end-bulbs  it  terminates  in 
the  interior  of  a  finely-granular  body,  the  so-called  inner  bulb. 

TACTILE  CELLS. 

The  tactile  cells  may  be  either  simple  or  compound.     The  simple  tac- 
tile cells  are  oval,  nucleated  bodies  measuring  from  6  to  12  /J.  (Fig.  123), 


Tactile  cell. 

Tactile  meniscus. 

Nerve-fiber.    _ 
Connective-tissue  sheath. 


Epidermis. 


Corium. 


FIG.  123.— FROM  A  VERTICAL  SECTION  OF  THE  SKIN  OF  THE  GREAT  TOE  OF  A  MAN  TWENTY-FIVE 
YEARS  OLD.  X  240.  The  outlines  of  the  cells  and  nuclei  of  the  epidermis  can  only  be  indistinctly 
seen,  x,  Tactile  cells  in  the  corium,  resting  upon  the  ramifications  of  a  delicate  nerve-fiber. 
Techn.  No.  82. 


I92 


HISTOLOGY. 


which  occur  in  the  deepest  strata  of  the  epidermis  and  the  outer  root- 
sheath  of  the  hairs  or  in  the  adjacent  portions  of  the  corium.  The  tac- 
tile cells  rest  on  the  tactile  meniscus,  a  crescentic  expansion  of  a  non- 
medullated  nerve-fiber. 

The  compound  tactile  cells  (Grandry's  and  Merkel's  corpuscles)  con- 
sist of  two  or  more  somewhat  flattened  cells,  each  larger  than  a  simple 
tactile  cell  (15  ta  deep  and  50  /i  wide)  that  contain  a  vesicular  nucleus. 
A  medullated  nerve-fiber  approaches  the  compound  tactile  cells  (Fig. 
124)  and  the  forks  of  the  divided  axis-cylinder  clasp  a  flat  disc,  the 


is 


FIG.  124. — FROM  VERTICAL  SECTIONS  OF  THE  SKIN  OF  THE  BEAK  OF  A  GOOSE.  X  240.  A.  Com- 
pound tactile  cell  (simple  tactile  corpuscle),  cut  parallel  to  the  course  of  the  entering  nerve-fiber  : 
n.  medullated  nerve-fiber  only  partially  met  by  the  section  ;  a,  axis-cylinder:  its  division  is  here,  in 
profile,  invisible;  fs,  tactile  discs  cut  vertically;  h,  connective-tissue  sheath;  tz,  tactile  cells. 
B.  Two  compound  tactile  cells  cut  transversely  to  the  plane  of  the  entering  nerve-fiber  :  i.  "  Simple 
tactile  corpuscle,"  consisting  of  four  tactile  cells;  2,  twin  tactile  cells;  is,  tactile  discs;  a.  axis- 
cylinders  in  transverse  section,  before  dividing;  n,  medullated  nerve-fibers;  c,  corium.  Techn. 
No.  83. 

tactile  disc  (fc),  that  lies  between  two  flattened  cells  (tz).  The  nerve-fiber 
loses  its  medullated  sheath  at  the  point  of  entrance  and  the  neurilemma 
becomes  fused  with  the  connective  tissue  of  the  capsule  (//)  enveloping 
the  tactile  cells.  The  compound  forms  consisting  of  two  tactile  cells 
are  named  twin  tactile  cells  (B  2),  those  containing  three  or  four  tactile 
cells,  "simple  tactile  corpuscles."  The  compound  tactile  cells  have 
only  been  found  in  the  epidermis  of  the  beak  and  in  the  tongue  of  birds, 
especially  in  web-footed  birds  ;  they  are  almost  exclusively  situated  in 
the  uppermost  strata  of  the  corium. 

END-BULBS. 

The  end-bulbs  are  spherical  or  oval  bodies  in  the  interior  of  which 
nerve-fibers  terminate,  sometimes  in  a  simple,  sometimes  in  a  branched 
ending.  There  are  various  forms  of  end  bulbs. 

The  so-called  cylindrical  end-bulbs,  the  simplest  form,  chiefly  consist 
of  a  modified  extension  of  the  entering  nerve-fiber  and  comprise  three 
parts, — the  axis-cylinder,  the  inner  bulb,  and  the  capsule.  The  capsule  is 
comoosed  of  flattened  connective-tissue  cells,  the  continuation  of  the 


THE    PERIPHERAL    NERVOUS    SYSTEM. 


193 


fiber-sheath.  The  inner  bulb  is  a  finely-granular  mass  which  exhibits 
concentric  stratification  and  a  few  nuclei  at  the  periphery.  The  nerve- 
fiber  loses  its  medullary  sheath  on  entering  the  inner  bulb,  in  which  the 
axis-cylinder  ascends  as  a  flat  band  and  terminates  at  the  upper  pole  in 
a  free  or  club-shaped  ending.  The  cylindrical  end-bulbs  are  found  in  the 
tunica  propria  of  mucous  membranes  ;  for  example,  in  the  scleral  con- 
junctiva of  mammals  and  in  the  oral  mucous  membrane. 

The  lamellar  corpuscles  (Vater,  Pacini)  are  transparent,  elliptical 
structures,  from  2  to  3  mm.  long  and  I  to  2  mm.  thick,  and,  like  the 
cylindrical  end-bulbs,  consist  of  a  capsule,  an  inner  bulb,  and  an  axis- 
cylinder.  The  latter  possess  the  same  structure  as  in  the  end-bulbs,* 


Blood-vessel. 

Axis-cylinder. 
Inner  bulb. 
Sheath. 


Medullated 

nerve-fiber. 


ii 


FIG.  125.— CYLINDRICAL  END-BULB  FROM  THE  CON- 
JUNCTIVA OF  A  CALF.     X  240.     Techn.  No.  84. 


^ Axis-cylinder. 


Inner  bulb. 


FIG.  126.— SMALL  LAMELLAR  CORPUSCLE  FROM  THE 
MESENTERY  OF  A  CAT.  X  50.  The  cells  lining  the 
capsules  may  be  recognized  by  their  prominent 
nuclei.  The  medulla  of  the  nerve-fiber  may  be 
traced  to  the  inner  bulb.  Techn.  No.  85. 


but  the  capsule  is  differently  formed.  It  consists  of  a  large  number  of 
concentric  capsules,  or  lamellae,  each  lined  by  a  simple  layer  of  endo- 
thelioid  cells  and  separated  from  neighboring  lamellae  by  a  serous  fluid. 
Each  lamella  consists  of  an  outer  transverse  and  an  inner  longitudinal 
layer  of  connective-tissue  fibers.  As  the  capsule  of  the  end-bulbs,  so 
also  these  capsules  originate  from  the  connective-tissue  sheath  of  the 
entering  nerve-fiber.  They  are  the  smaller  the  nearer  they  lie  to  the 
inner  bulb.  Along  the  course  by  which  the  entering  nerve  passes  to 
the  inner  bulb  the  lamellae  are  not  infrequently  united  by  a  longitudinal 


*  In  the  lamellar  corpuscles  the  axis-cylinder  not  infrequently  is  forked  at  its  extremity  or 
it  breaks  up  into  several  twisted  interlacing  twigs. 
13 


194  HISTOLOGY. 

strand  of  tissue,  the  inter  Lamellar  ligament.  A  small  artery  accompanies 
the  nerve-fiber  into  the  interior  of  the  corpuscle,  which  breaks  up  into  a 
capillary  network  lying'  between  the  peripheral  lamellae. 

The  lamellar  corpuscles  partly  occur  in  superficial  situations,  abun- 
dantly in  the  subcutaneous  connective-tissue  of  the  palm  of  the  hand  and 
the  sole  of  the  foot,  more  sparingly  in  other  areas  of  the  skin,  in  the 
nipples,  in  the  territory  of  the  pudendal  nerve,  partly  in  deeper  situations, 
in  the  vicinity  of  the  joints,  on  the  nerves  of  the  periosteum  and  the 
bones,  and  in  the  neighborhood  of  the  pancreas,  in  the  mesentery. 

The  corpuscles  of  Herbst  and  Key-Retzius,  occurring  in  birds, 
are  also  lamellar  corpuscles  ;  they  only  differ  in  being  much  smaller  and 
in  possessing  a  double  row  of  longitudinally-disposed  nuclei  in  the  inner 
bulb. 

Tht  genital  nerve-corpuscles  of  the  lower  mammals  and  of  man  are 
spherical  or  oval  forms  (from  0.06  mm.  to  0.4  mm.  long),  and  consist  of  a 
finely-granular,  nonnucleated  inner  bulb  enveloped  in  a  connective  -tissue 
capsule  containing  cells  rich  in  protoplasm.  The  approaching  medullated 
nerve-fibers  make  several  turns  around  the  corpuscle,  lose  their  medulla 
and  divide,  while  fiber-sheath  and  neurilemma  pass  into  the  capsule  ;  the 
naked  axis-cylinders  penetrate  the  inner  bulb  at  different  points,  undergo 
rapid  division  and  form  a  dense  plexus  of  fibrils  with  varicose  enlarge- 
ments. In  imperfect  staining  the  varicosities  simulate  club-shaped  endings. 
Each  plexus  is  joined  to  neighboring  plexuses  by  delicate  nerve  filaments. 

The  genital  corpuscles  lie  in  the  depths  of  the 
corium  at  various  distances  from  the  papillary 
stratum  ;  in  the  papillae  only  smaller  corpuscles, 
resembling  the  "  spherical  end-bulbs,"  are  found. 
The  largest  number,  from  one  to  four  to  the 
square  millimeter,  occurs  in  the  glans  penis  and 
in  the  clitoris.  The  so-called  spherical  end-bulbs 
(they  are  sometimes  round,  sometimes  oval)  have 
a  similar  structure  ;  they  are  found  in  the  con- 
junctiva and  in  the  adjoining  portions  of  the 

FIG  i27  -TACTILE  CORPUSCLE  cornea  of  man'  and  Possess  a  greatest  diameter 
of  °'°2  to  a  1  "^  The  ™'ticular  ncrve-cor- 
puscles  belong  to  the  same  category. 

The  tactile  corpuscles  (Wagner's  and  Meiss- 


The     nuclei      are     invisible.  ,       N  ...       .       ,  r 

Techn.  NO.  82.  ner  s  corpuscles)  are  elliptical  structures,  trom 

40  to  100  p-  long  and   30  to  60  p-  broad,  which 

are  characterized  by  cross-markings.     They  possess   a  connective-tissue 
capsule  (Fig.  127,  Ii)  with   flattened   cells,   the  boundaries  of  "which,  as 


THE    PERIPHERAL    NERVOUS    SYSTEM. 


195 


well  as  their  transversely-placed  nuclei,  produce  the  cross-striations  just 
mentioned.  One  or  two  medullated  nerve-fibers  approach  each  tactile 
corpuscle  (Fig.  127,  ;/),  make  transverse  tours  encircling  the  lower  pole 
of  the  corpuscle,  part  with  their  neurilemma  and  fiber-sheath,  which 
blend  with  the  tissue  of  the  capsule,  then  lose  their  medullary  sheath, 
and  as  naked  axis-cylinders  enter  into  a  granular  substance  corresponding 
to  an  inner  bulb  ;  there  they  form  a  complicated  plexus  beset  with  vari- 
cosities  (V).*  These  tactile  corpuscles  lie  in  the  papillae  of  the  corium  and 
are  most  numerous  (twenty-three  to  one  square  millimeter)  on  the  palm 
of  the  hand,  on  the  finger-tips,  and  on  the  sole  of  the  foot. 

TERMINATIONS  OF  THE  MOTOR  NERVES. 

The  small  nerve -trunks*  supplying  striated  muscle  divide  into 
branches,  these  subdivide  into  twigs  (nerve-fiber  bundles)  that  anasto- 
mose with  one  another  and  form  a  plexus,  the  intermuscular  plexus.  In 
the  compass  of  this  plexus  the  medullated  nerve -fibers  undergo  numer- 
ous divisions,  so  that  the  number  of  nerve-fibers  is  considerably  increased. 


Sensory   nerve- 
fibers. 


Muscle-fibers 


Medullated 
nerve-fibers. 


FIG.  128. — MOTOR  NERVK-ENDINGS  OF   INTERCOSTAL    MUSCLE-FIBERS  OF  A   RABBIT     X  150 

Techn.  No.  86  a. 

From  the  small  bundles  of  the  plexus  single  delicate  nerve-fibers  spring, 
each  one  of  which  finally  connects  with  a  muscle-fiber.  At  the  point 
where  the  nerve-fiber  comes  into  contact  with  the  muscle-fiber  it  loses  its 
medullated  sheath,  the  axis-cylinder  breaks  up  into  a  number  of  slightly  - 


*  In  imperfect  staining  the  varicosities  simulate  club-shaped  endings. 


196  HISTOLOGY. 

tortuous  terminal  branches  with  bulbous,  swollen  extremities,  which 
form  the  so-called  motor  end-plate  and  rest  upon  a  rounded,  finely- 
granular  disc  (sole-plate]  containing  numerous 
vesicular  nuclei.  Each  muscle-fiber  possesses 
at  least  one  motor  end-plate  ;  whether  they  lie 
upon  or  under  the  sarcolemma  is  not  yet  defi- 
nitely determined. 

The  nerves  supplying  the  smooth  muscles 
form    a    plexus    from    which     bundles    of   non- 
FIG.  I29.-MOTOR  NERVED-     medullated  nerve-fibers  arise;   the  latter  divide 
repeatedly    and    form     several    networks,    from 


%  ,Sr  Tthe  ndYsce"fiTeh^     which  spring  the  most  delicate  nerve-fibers.  They 

transverse  striae  are  distinct  1-11  ..1  ,1  i       ru  j 

only  in  the  lower  hair  of  the     apply  themselves  to  the  smooth  muscle-fibers  and 

muscle-fiber.  Techn.  No.  86  b.  r  ..     .  r 

often  are  slightly  thickened  at  the  point  of  contact. 


THE   SUPRARENAL  BODY. 

The  description  of  the  suprarenal  body  with  the  organs  of  the 
nervous  system  is  warranted  by  the  profusion  of  its  nervous  elements, 
by  its  relations  to  the  central  nervous  system,  as  established  by  experi- 
ment, as  well  as  by  the  facts  of  comparative  anatomy. 

Each  suprarenal  body  consists  of  a  cellular  parenchyma  and  a 
connective-tissue  capsule,  which  sends  delicate  processes  into  the  interior 
of  the  organ.  The  parenchyma  consists  of  an  outer  stratum,  the  cortex, 
which  surrounds  an  inner  mass,  the  medulla,  on  all  sides.  The  cortex 
in  the  fresh  state  is  of  a  yellow  color  and  is  composed  of  groups  of  cells 
about  15  fj.  in  size,  rounded  in  shape,  that  possess  a  coarsely-granular 
protoplasm,  sometimes  containing  fat  particles,  and  a  clear  nucleus.  In 
the  outer  zone  of  the  cortex  the  cells  are  grouped  in  oval  masses  ;  in  the 
middle  zone  they  are  arranged  in  cylindrical  columns,  while  in  the  inner- 
most zone  the  anastomosing  cords  of  cells  lie  irregularly  scattered  in  a 
reticulum  of  connective-tissue  ;  the  cells  of  the  innermost  zone  are  char- 
acterized by  their  pigmentation.  According  to  the  described  arrange- 
ment the  cortex  is  divided  as  follows:  I,  the  zona  glomernlosa ;  2,  the 
zona  fasciculata  ;  3,  the  zona  reticularis.  The  medulla  in  the  fresh  state 
is  sometimes  lighter,  sometimes  darker  than  the  cortex  ;  it  consists  of 
polygonal  cells  *  possessing  a  finely-granular  protoplasm  and  a  clear 


*  Whether  these   cells  are   gland-cells  that  discharge  their  secretion  into  the  veins  is  a 
question  that  demands  further  investigation. 


THE    PERIPHERAL    NERVOUS    SYSTEM. 


197 


nucleus.     They  are  arranged  in  spherical  groups  or  oval  cords  joined  in 
an  irregular  network. 

The  arteries  divide  in  the  connective-tissue  capsule  into  numerous 
small  branches,  that  penetrate  the  cortex  and  there  form  a  long-meshed 
capillary  network,  which  passes  into  the  medullary  substance  where  the 
meshes  are  round.  From  the  latter  the  veins  proceed,  of  which  the 
larger  are  accompanied  by  longitudinal  strands  of  smooth  muscle-fibers. 
While  still  within  the  medulla  the  veins  unite  and  form  the  chief  vein, 
the  suprarenal  vein. 

~~-        ax     ----  --_  __  ?—^-  \Caps\ile. 


Zona  glomerulosa. 


Zona  fasciculata. 


Zona  reticularis. 


Cords  of  cells  of  the 
medulla. 


Nerve  in  transverse 
section. 


Cortex. 


Ganglion-cells. 


Medulla 


Bundles  of  smooth  mus 
cle-fibers  in  transverse 
section.  |B 

Veins  in  cross-section.^" 

Cortex.     Medulla.     Vein. 
A 

FIG.  130. -A.  SECTION  OF  THE  SUPRARENAL  BODY  OF  A  CHILD.    X  15.    Techn.  No.  87.    B.  SECTION  OF 
A  HUMAN  SUPRARENAL  BODY.     X  50.    Techn.  No.  89. 

The  numerous,  chiefly  nonmedullated  nerves  (in  man  about  33  small 
trunks)  come  principally  from  the  celiac  plexus  and  pass  with  the  arteries 
through  capsule  and  cortex  to  the  interior  of  the  medulla.  During 
this  course  they  give  off  a  few  twigs  to  the  capsule,  that  form  a  plexus 
there  ;  from  this  delicate  branches  descend  into  the  cortex  between  the 
cell-groups  of  the  zona  glomerulosa  and  fasciculata,  which  terminate  on 
the  surface  of.  the  cell-clusters,  without  penetrating  between  the  indi- 
vidual cells.  Richer  is  the  nerve -plexus  of  the  zona  reticularis,  which 
originates  by  the  branching  of  fibers  that  descend  straight  through  the 
cortex  ;  it  also  surrounds  only  cell-groups.  In  the  medullary  substance 
the  nerve-plexus  is  extraordinarily  dense  ;  each  individual  cell  is  sur- 


198 


HISTOLOGY. 


rounded  by  nerve-fibers.  In  the  medullary  substance,  seldom  in  the 
cortex,  groups  of  sympathetic  ganglion-cells  occur.  Some  of  the  nerves 
terminate  in  the  walls  of  the  blood-vessels. 


*''" 


Capsule. 


a  glomerulosa. 


?&&*  -.«!«/'.  ,.  . 


/ Zona  fasciculata. 


Zona  reticularis. 


> Medulla. 


I 


FIG.  131.— SECTION  THROUGH  CORTEX  AND  MEDULLA  OF  THE  SUPRARENAL   BODY  OK  ADULT  MAN. 

X  200.     (Schaper.) 


THE    PERIPHERAL    NERVOUS    SYSTEM.  199 


TECHNIC. 

No.  67. — The  Spinal  Cord. — For  the  study  of  the  distribution  of 
the  white  and  the  gray  substance  the  spinal  cord  of  a  child  should  be 
fixed  in  toto  in  about  one  liter  of  Miiller's  fluid,  that  should  be  fre- 
quently changed  ;  after  four  or  five  months  thick  cross-sections  of  the 
cervical,  thoracic,  and  lumbar  regions  may  be  cut,  and  without  further 
treatment  mounted  in  dilute  glycerol  (p.  22),  or  after  the  customary 
preliminary  treatment  they  may  be  mounted  in  damar. 

No.  68. — The  Spinal  Cord ;  Staining  of  Medullated  Fibers,  after  Pal. 
— The  success  of  the  preparation  depends  especially  on  the  state  of 
preservation  of  the  organ.  The  fresher  the  tissue  when  it  is  put  into  the 
fixing  fluid,  the  better  will  be  the  result.  The  entire  spinal  cord  should 
be  placed  in  a  large  quantity  of  Miiller's  fluid,  that  must  be  changed 
daily  during  the  first  week  and  frequently  thereafter.  If  it  is  desired  to 
investigate  only  portions  of  the  spinal  cord,  then  place  pieces  of  the  fresh 
cord  about  2  cm.  long,  taken  from  the  lower  cervical,  the  middle  thoracic, 
and  the  lumbar  region,  in  200  to  500  c.c.  of  Miiller's  fluid  or,  better,  sus- 
pend them  in  it.  In  four  or  six  weeks,  during  which  time  the  fluid  must 
be  frequently  changed,  the  tissue  is  to  be  transferred  directly,  without 
previous  washing,  to  I  50  c.c.  of  70  per  cent,  alcohol  and  on  the  follow- 
ing day  to  the  same  quantity  of  90  per  cent,  alcohol.  The  bottle  con- 
taining the  tissue  must  be  placed  in  the  dark  (p.  33),  and  the  alcohol  be 
frequently  changed  during  the  first  eight  days.  Sections  may  then  be 
cut.  The  sections  are  to  be  placed  in  a  capsule  containing  20  c.c.  of  70 
per  cent,  alcohol,  and  as  soon  as  possible  transferred  from  this  to  30  c.c. 
of  Weigert's  hematoxylin  to  which  i  c.c.  of  lithium  carbonate  solution 
has  been  added  (p.  24).  In  five  or  six  hours  the  now  very  dark,  un- 
transparent  sections  should  be  transferred  to  50  c.c.  of  distilled  water 
plus  i  c.c.  of  lithium  carbonate  solution.  In  a  half-hour,  during  which 
time  the  fluid  must  be  changed  several  times,  the  sections  will  give  off 
no  more  color  and  are  then  to  be  placed  in  30  c.c.  of  potassium  perman- 
ganate solution  for  differentiation  (p.  24).  In  from  one-half  to  three 
minutes  the  sections  are  to  be  washed  for  one  minute  in  distilled  water 
and  then  transferred  to  20  c,c.  of  the  acid  mixture  (p.  24).  The  capsule 
containing  the  acid  mixture  should  be  covered.  The  decolorization 
occurs  in  from  ten  to  fifty  seconds  ;  the  gray  substance  becomes  light 
yellow,  almost  white,  the  white  substance  (the  medullated  nerve-fibers) 
appears  very  dark.  Now  transfer  the  sections  to  a  capsule  containing 
30  c.c.  of  distilled  water  and  in  five  minutes  to  a  second  capsule  contain- 
ing the  same  quantity  of  fresh  distilled  water.  .  After  ten  minutes  place 
them  in  10  c.c.  of  alum-carmine,  in  which  they  may  remain  from  three  to 
fifteen  hours.  Mount  in  damar.  The  alum-carmine  staining  may  be 
omitted. 

The  foregoing  directions  are  intended  for  thin,  well-fixed  prepara- 
tions. If  the  sections  are  thick,  if  the  tissue  has  lain  a  long  time  in 
alcohol,  more  time  will  be  required  for  staining  and  reduction.  Should 


2OO  HISTOLOGY. 

they  not  stain,  place  unstained  sections  in  Miiller's  fluid  for  twenty-four 
hours,  wash  one  minute  in  distilled  water,  then  stain,  and  the  result  may 
be  successful.  Should  the  decolorization  be  insufficient,  if  the  gray  sub- 
stance does  not  become  yellowish- white,  the  procedure  may  be  repeated  ; 
that  is,  the  sections  are  to  be  again  placed  in  distilled  water  one  minute, 
then  in  potassium  permanganate  one  or  three  minutes,  then  in  distilled 
water  one  minute,  and  finally  in  the  acid  mixture.  The  given  quantities 
of  the  permanganate  solution  and  of  the  acid  mixture  are  sufficient  for 
only  a  few,  about  20  sections.  If  it  is  desired  to  treat  more  sections, 
larger  quantities  of  these  fluids  must  be  used. 

No.  69. — The  Spinal  Cord ;  Staining  of  Axis-cylinders  and  of  Cells. 
— Place  pieces  at  the  most  2  cm.  long  in  200  c.c.  of  Muller's  fluid,  that 
must  be  changed  daily  during  the  first  week  and  once  a  week  thereafter. 
In  four  weeks  transfer  the  tissue  directly  from  Muller's  fluid  to  about 
50  c.c.  of  sodium  carminate  (i  per  cent,  aqueous  solution),  in  which  it 
should  remain  for  three  days.  During  this  time  the  bottle  containing  the 
tissue  must  be  frequently  shaken.  The  stained  pieces  are  to  be  washed  for 
twenty -four  hours  in  running  water,  then  placed  in  150  c.c.  of  70  per 
cent,  alcohol,  and  after  five  hours  transferred  to  the  same  quantity  of  95 
per  cent,  alcohol.  Mount  the  cross-sections  in  damar  (Fig.  100). 

No.  70. — Spinal  Cord ;  Golgi  Staining* — The  length  of  time  the 
tissue  must  remain  in  the  Golgi  mixture  depends  upon  the  elements  it  is 
desired  to  stain, f  as  follows  : — 

Two  to  three  days  for  neuroglia-cells. 

Three  to  five  days  for  nerve-cells. 

Five  to  seven  days  for  nerve-fibers  (collaterals). 

For  this  purpose  take  the  spinal  cord  with  the  vertebral  column  of  a 
newborn  rat  or  mouse,  and  treat  it  according  to  the  method  given  on 
page  41.  Since  the  pieces  must  be  used  as  soon  as  they  are  taken  out 
of  the  silver  solution,  only  one  piece  at  a  time  should  be  transferred  to 
the  absolute  alcohol.  Cut  the  sections  through  the  spinal  cord  and  the 
vertebral  column. 

The  spinal  cord  of  a  three-  or  seven -day-old  embryo  chick  furnishes 
still  better  results,  but  it  is  necessary  to  embed  the  tissue  in  celloidin 
(see  Microtome  Technic).  The  spinal  cord  of  kittens  as  well  as  that  of 
human  embiyos  20  to  40  cm.  long  yields  very  useful  results. 

No.  71. —  The  Brain  ;  Staining  of  Medullated  Nerve-fibers. — Apply 
the  method  given  in  No.  68.  If  an  entire  human  brain  is  to  be  placed 

*  Editor's  remark  :  The  application  of  the  Cox- Golgi  mixture,  in  the  manner  described 
on  p.  41,  footnote,  is  also  highly  recommended.  Since  it  can  be  applied  with  good  results  to  the 
central  nervous  system  of  adidt  animals,  it  offers,  in  the  manipulation  of  the  material  and  the 
preparation  of  the  sections,  valuable  advantages,  particularly  to  the  beginner.  After  the  treat- 
ment with  alcohol  the  larger  pieces,  without  being  embedded,  can  be  easily  cut  freehand,  when 
thick  sections  are  desired. 

flf  the  action  of  the  mixture  is  too  brief  the  central  portions  of  the  sections  appear  un- 
transparent  and  penetrated  by  abundant  precipitates  ;  if  the  action  of  the  mixture  is  too  pro- 
longed the  resulting  impregnation  of  the  elements  will  be  unsatisfactory. 


THE    PERIPHERAL    NERVOUS    SYSTEM.  2OI 

in  Miiller's  fluid,  many  deep  incisions  should  be  made  in  it  and  about  3 
liters  of  the  fixing  fluid  should  be  used. 

No.  72. — The  Brain  ;    Cells. — Treat  pieces  I  or  2  cm.  square  of  the 
cerebral   cortex  (paracentral  convolution)  and  of  the  cerebellar  cortex 
like   No.   69.      In   the    cerebral   cortex,   in 
addition  to  the  cell-forms  described,  an  ex- 
tremely variable  number  of  vesicular  spaces  ^ 
containing    remnants  of  cells   (protoplasm 
and  nucleus)  may  be  seen  (Fig.    132,  z]  ; 
they  are  probably  pericellular  lymph-spaces, 
which  by  post-mortem    alteration  and  the             ?           ,01 
influence  of  the  fixation  medium  have  be- 
come abnormally  enlarged.     The  sections              </.-—- 
through    the    cerebellar    cortex    must    be 
made  transverse  to  the    long  axis  of  the      FIG  I32._PoRTION  OF  A  SECTION  OF 

Convolutions,  since  the  ramifications  of  the  HUMAN  CEREBRAL  CORTEX.    X  240. 

'    .     .  .  ,  p,  Small  pyramidal  cells ;  a,  the  nerve- 

cells   of    rurkinje    extend    only    in    planes        process  of  a  pyramidal  ceil. 

transverse    to    the    convolution.       Only    a 

few  cells  of  Purkinje   lie  in  the  depressions  between  the   convolutions. 

No.  73. — The  Brain;  Golgi  Staining* — a.  For  a  topographical 
view,  treat  the  brain  of  a  newborn  rat  or  mouse  in  the  unopened  cranium 
according  to  the  method  given  in  No.  70.  The  cranium  may  be 
sectioned  with  the  brain-substance. 

b.  For  specimens  of  the  cortex,  the  brain  of  a  mouse  from  eight  to 
thirty  days  old  is  most  suitable,  treated  with  the  Golgi  mixture  for  from 
two  to  three  days,  or  of  a  one-  to  fifteen-day-old  rabbit  or  a  kitten  under 
six  weeks  old,  treated  with  the  Golgi  mixture  for  five  days.  Pieces  of 
the  brain  of  adults  must  remain  in  the  Golgi  mixture  for  from  eight  to 
fifteen  days.  Further  treatment  like  No.  70. 

No.  74. — The  Cortex  of  tlie  Cerebellum;  Golgi  Staining* — Remove 
the  cerebellum  from  the  cranium  of  a  newborn  guinea-pig  (or  a  kitten 
less  than  six  weeks  old)  and  treat  it  according  to  the  method  given  in  No. 
70.  The  staining  of  the  elements  of  the  cerebellum  is  more  difficult  to 
accomplish  than  of  those  of  the  cerebrum  and  the  spinal  cord.  Failures 
are  frequent.  The  sections  should  be  principally  made  vertically  to  the 
axis  of  the  convolutions.  (For  embedding,  see  Microtome  Technic.) 

No.  75. — Hypophysis  Cerebri. — Treat  like  No.  80. 

No.  76. — Brain-sand,  Acervulus  Cerebri. — Tease  the  epiphysis  in  a 
drop  of  salt  solution.  If  much  brain-sand  is  present,  a  gritty  sound  will 
be  heard  on  teasing  and  the  larger  concretions  can  be  perceived  by  the 
unaided  eye.  Examine  with  the  low  power,  without  a  cover-glass  (Fig. 
114);  the  granules  are  not  always  round,  but  often  oval  and  dentated  ; 
occasionally  the  irregularity  of  the  surface  is  indistinct,  because  they  are 


*  For  the  application  of  the  Cox-Golgi  mixture  see  p.  41  and  200,  remark. 


2O2  HISTOLOGY. 

enveloped  in  concentrically-arranged  connective-tissue  fibers.  Push  aside 
the  larger  granules  with  a  needle,  cover  a  few  of  the  smaller  ones  with  a 
cover-glass  and  treat  with  2  to  3  drops  of  hydrochloric  acid  (p.  48). 
Bubbles  of  gas  develop  and  the  sharp  outlines  of  the  granules  disappear. 

No.  77. — Corpuscula  Amylacea, — Select  the  brains  of  elderly  indi- 
viduals. With  a  scalpel  scrape  the  mesial  surface — that  directed  toward 
the  third  ventricle — of  the  optic  thalamus  and  spread  the  scrapings  with 
a  needle  in  a  drop  of  salt  solution  ;  apply  a  cover-glass.  The  corpuscles 
when  present  are  easily  found,  and  are  recognized  by  their  bluish-green 
color  and  their  stratification  (Fig.  115,^).  They  must  not  be  confused 
with  drops  of  extruded  myelin  (£),  which  are  always  clear  and  have  a 
double  contour.  In  addition  there  are  found  in  such  preparations 
numerous  red  blood-corpuscles,  ependymal  cells  (d),  medullated  nerve- 
fibers  varying  in  thickness,  and  ganglion-cells  ;  the  latter  are  very  pale 
and  often  can  only  be  detected  by  their  pigmentation  (/).  Human 
brains,  even  though  not  absolutely  fresh,  are  still  useful. 

No.  78. — a.  Spread  out  a  piece  I  cm.  long  of  the  cJwroid plexus  in 
a  drop  of  salt  solution  and  apply  a  cover-glass.  The  convoluted  red 
blood-vessels  and  the  epithelium  of  the  plexus  can  be  seen. 

b.  Very  pretty  permanent  preparations  maybe  obtained  as  follows  : 
Carefully  spread  out  a  little  piece  of  the  plexus  in  salt  solution  ;  if  good 
fields  are  visible  with  the  low  power,  let  the  salt  solution  flow  off  and  add 
a  few  drops  of  Zenker's  fluid  (p.  21)  ;  then  apply  a  cover-glass,  at  the 
edge  of  which  place  a  little  more  of  the  Zenker's  fluid.  After  thirty 
minutes  displace  this  fluid  by  distilled  water,  and  after  another  thirty 
minutes  the  water  by  50  per  cent,  alcohol  to  which  a  few  drops  of  tinct- 
ure of  iodin  have  been  added.  In  fifteen  minutes  take  off  the  cover- 
glass  and  transfer  the  now  fixed  preparation  to  a  watch-glass  with  fresh 
50  per  cent,  iodin-alcohol,  to  which,  in  case  it  becomes  rapidly  decolor- 
ized, tincture  of  iodin  is  to  be  added.  In  from  fifteen  to  thirty  minutes 
transfer  the  object  to  pure  70  per  cent,  alcohol,  and  after  about  twelve 
hours  stain  it  with  hematoxylin  and  eosin  (p.  37)  and  mount  in  damar 
(P-  45). 

No.  79. — Transverse  Sections  of  Nerve -fiber  Bundles. — Treat  apiece 
of  nerve,  if  possible  the  sciatic  of  man,  that  possesses  a  well-developed 
endoneurium,  according  to  the  method  given  in  No.  32.  Place  it  for  six 
days  in  a  o.  I  per  cent,  solution  of  chromic  acid,  then  wash  it  for  from 
three  to  four  hours  in  running  water,  and  harden  it  in  gradually- 
strengthened  alcohol.  When  the  hardening  is  completed,  cut  thin  sec- 
tions with  a  sharp  razor.  It  is  advisable  to  embed  the  tissue  in  liver  ; 
better  still,  in  elder-pith  or  in  the  pith  of  the  sunflower.  For  this  pur- 
pose, make  a  hole  in  the  dry  elder-pith  with  a  needle,  and  then  carefully 
insert  the  nerve.  Place  the  whole  for  about  a  half-hour  in  water ;  the 
pith  swells  and  firmly  grasps  the  nerve.  Stain  the  sections  in  picrocar- 
mine  and  mount  in  glycerol.  The  length  of  time  required  for  staining 
varies  greatly.  The  sections  must  be  very  carefully  handled  and  pressure 


THE    PERIPHERAL    NERVOUS    SYSTEM. 


203 


with  the  cover-glass  must  be  scrupulously  avoided,  lest  the  sections  of 
the  fibers,  which  are  not  discs,  but  short  cylinders,  be  turned  on  their 
sides,  and  not  a  fiber  in  section  be  seen.  If  successful,  the  section  will 
show  a  somewhat  shrunken  axis-cylinder,  resembling  a  red  nucleus,  sur- 
rounded by  the  yellow  medulla,  which  is  enclosed  by  the  reddish  neuri- 
lemma.  The  cross-section  of  the  nerve-fiber  has  been  compared  to  a 
picture  of  the  sun  (Sonnenbtldchenfigur)  (Fig.  133). 


Epineurium. 


FIG.  133.— FROM  A  TRANSVERSE  SECTION  OF  A  PERIPHERAL  (SPINAL)  NERVE  OF  RABBIT.  X  50.  In  the 
lower  funiculus,  on  the  right,  some  of  the  transverse  sections  of  nerve-fibers  have  fallen  out,  others 
are  lying  on  one  side,  as  a  consequence  of  pressure.  In  the  rabbit  the  endoneurium  is  only  slightly 
developed. 

No.  80. — Spinal  Ganglia. — These  are  difficult  to  obtain.  Therefore 
remove  the  Gasserian  ganglion  from  the  depression  in  which  it  is  lodged 
(on  the  anterior  surface  of  the  petrous  portion  of  the  temporal  bone),  and 
place  it  in  about  100  c.c.  of  Muller's  fluid  for  fixation.*  After  four  weeks 
wash  it  for  three  hours  in  running  water  and  harden  it  in  50  c.c.  of 
gradually-strengthened  alcohol  (p.  33).  Cut  the  thinnest  possible  trans- 
verse and  longitudinal  sections ;  stain  them  thirty  seconds  in  hema- 
toxylin,  then  from  two  to  five  minutes  in  eosin  (p.  37,  3  <£),  and  mount  in 
damar.  The  ganglion-cells  are  pale  red  ;  the  axis-cylinder  deep  red  ; 
the  medullary  sheath  brownish  ;  the  nuclei  blue  (Fig.  1 19  and  Fig.  120). 
If  the  section  is  not  sufficiently  thin,  the  large  number  of  deeply-stained 
nuclei  will  render  it  difficult  to  see  the  other  structures.  For  this  reason 
it  is  better  to  stain  thick  sections  in  picrocarmine,  two  or  three  days,  and 
mount  them  in  damar.  The  nuclei  are  then  not  so  intensely  stained. 
Occasionally  the  protoplasm  of  the  ganglion-cell  contracts,  and  thus- 
acquires  a  stellate  outline  (Fig.  120,  x),  that  may  easily  lead  the 
beginner  to  confuse  it  with  a  multipolar  ganglion-cell. 

T-shaped  branches  may  be  seen  in  preparations  of  the  spinal  cord 
treated  after  No.  70.  In  young  embroyo  chicks  the  spinal  ganglion- 
cells  are  still  bipolar.  Unipolar  cells  are  found  in  embryo  chicks  about 


*  Fixation  in  Kleinenberg's  picrosulphuric  acid  also  gives  very  good  results. 


204  HISTOLOGY. 

seventeen  days  old,  transition  forms  between   the  ninth  and  fourteenth 
days,  and  in  embryo  rabbits  from  5  to  1 2  cm.  long. 

No.  8 1. — Sympathetic  Ganglia. — Fix  and  harden  the  large  superior 
cervical  ganglion  of  the  sympathetic  nerve  like  No.  80.  Here,  too,  on 
account  of  the  abundance  of  nuclei,  nuclear  staining  is  applicable  only  to 
very  thin  sections.  Treated  according  to  the  method  given  in  No.  80,  the 
processes  of  the  multipolar  ganglion-cells  are  not  rendered  distinct.  For 
this  purpose  place  the  thinnest  possible  sections  for  twenty-four  hours  in 
5  c.c.  of  nigrosin  solution  (prepared  like  the  methyl-violet  solution, 
p.  25);  then  transfer  them  to  5  c.c.  of  absolute  alcohol  for  five  minutes, 
and  preserve  in  damar.  The  characteristic  bundles  of  nonmedullated 
nerve-fibers,  cut  obliquely  and  transversely,  can  be  recognized  with  the 
low  power ;  also  the  ganglion-cells  ;  but  to  see  their  processes  high 
magnification  and  careful  scrutiny  are  necessary  (Fig.  121).  In  many 
sections  the  processes  of  the  ganglion -cells  cannot  be  seen  ;  the  latter 
may  be  best  exhibited  according  to  the  method  given  in  No.  70,  and  a 
suitable  object  is  the  cervical  portion  of  a  ten-  or  fifteen-day-old  embryo 
chick. 

No.  82. — Simple  Tactile-Cells ;  Intra-cpithelial  Nerve-fibers  ;  Cells  of 
Langerlians  ;  Tactile  Corpuscles. — Prepare  a  mixture  of  gold  chlorid  and 
formic  acid  (p.  43),  boil  it  and  let  it  cool  ;  then  cut  from  the  volar  side 
of  a  freshly-amputated  finger  or  toe  (with  scissors  applied  flatwise)  sev- 
eral small  pieces  of  the  epidermis  and  uppermost  layers  of  the  corium 
about  5  mm.  long  and  I  mm.  broad.  Carefully  remove  any  fat  attached 
to  the  under  surface  of  the  corium  and  place  the  pieces  in  the  gold  and 
formic  acid  mixture  for  one  hour,  in  the  dark.  Then,  with  glass-rods, 
transfer  the  pieces  to  10  c.c.  of  distilled  water  and  in  a  few  minutes  to 
fresh  distilled  water  to  which  formic  acid  has  been  added  (p.  43),  and 
expose  the  whole  to  daylight  (sunlight  is  unnecessary).  In  from  twenty- 
four  to  forty-eight  hours  the  tissue  becomes  dark  violet.  It  is  now  to  be 
hardened  in  30  c.c.  of  gradually-strengthened  alcohol.  In  eight  days 
the  pieces  may  be  embedded  in  liver  and  sectioned  ;  mount  in  damar. 
The  epidermis  is  red-violet  in  different  tints  ;  the  nuclei  are  only  to  be 
seen  in  places  and  often  are  not  perceptible  ;  the  corium  is  white  ;  the 
capillaries,  the  excretory  ducts  of  the  coil -glands,  and  the  nerves  are  dark 
violet  to  black.  For  tactile  cells  the  thinnest  possible  sections  are  neces- 
sary. They  may  often  be  found  near  the  excretory  ducts  of  the  coil- 
glands.  Care  must  be  taken  not  to  confuse  them  with  shrunken  epithe- 
lial-cells (Fig.  123). 

The  intrar epithelial  nerve-fibers  appear  as  delicate  filaments  ;  their 
connection  with  the  nerve-fibers  in  the  corium  is  difficult  to  trace. 
Processes  of  the  cells  of  Langerhans,  in  thin  sections,  are  apt  to  be 
confused  with  the  intra-epithelial  nerve-fibers  (Fig.  122). 

The  cells  of  LangerJians  and  the  tactile  corpuscles  may  be  easily  seen  ; 
in  thick  sections  the  tactile  corpuscles  are  black  (Fig.  122),  in  thin  sec- 
tions red-violet  (Fig.  127). 

No.  83. — Compound  Tactile  Cells. — Cut  the  yellowish  wax-like  skin, 


THE    PERIPHERAL    NERVOUS    SYSTEM.  2O5 

or  cere,  from  the  lateral  edges  of  the  upper  beak  of  a  duck  or  goose  and 
treat  pieces  I  or  2  mm.  thick  and  I  cm.  long  with  3  c.c.  of  2  per  cent, 
osmic-acid  solution  plus  3  c.c.  of  distilled  water;  place  the  whole  in  the 
dark  from  eighteen  to  twenty-four  hours  ;  then  wash  the  pieces  for  one 
hour  in  running  water  and  transfer  them  to  20  c.c.  of  90  per  cent,  alcohol. 
In  six  hours  the  objects  may  be  sectioned.  Embed  them  in  liver  and 
make  the  sections  from  the  corium  toward  the  epithelium,  not  the 
reverse.  The  sections  may  be  mounted  unstained  in  damar.  The 
olive-green  tactile  cells  can  be  readily  seen,  but  the  entrance  of  the 
nerve-fiber  is  difficult  to  find  (Fig.  124).  In  addition,  Herbst's  corpuscles 
occur  in  the  sections.  If  it  is  desired  to  stain  the  sections,  use  a  nuclear 
staining  solution  (p.  36). 

No.  84. — Cylindrical  End-bulbs. — With  scissors  and  forceps  cut  out 
pieces  I  cm.  square  of  the  scleral  conj  unctiva  near  the  corneal  margin  of 
the  fresh  eye  of  a  calf,  taking  care  not  to  roll  them.  It  is  better  to  let 
them  lie  smooth  on  the  sclera.  Carefully  slip  the  pieces,  epithelial  side 
up,  from  the  sclera  on  to  a  cork-plate  and  span  them  out  with  needles. 
Moisten  the  surface  with  a  few  drops  of  the  vitreous  humor  obtained 
from  the  eye  of  the  calf;  with  scissors  and  forceps  dissect  off  a  thin  layer 
consisting  of  connective  tissue  and  the  epithelium  resting  upon  it.  This 
operation  must  be  done  with  great  care  ;  folding  and  torsion  of  the 
membrane  must  if  possible  be  avoided.  The  pieces,  with  the  epithelial 
side  up,  should  now  be  slipped  on  to  a  dry  slide  and  spread  out  flat.  At 
first  they  draw  together,  but  in  a  moment  or  two  the  edges  dry  some- 
what and  adhere  to  the  glass  and  they  can  then  be  extended  without 
much  difficulty.  The  slide  with  the  preparation  is  next  to  be  placed  in 
a  glass  jar  containing  65  c.c.  of  distilled  water  to  which  2  c.c.  of  acetic 
acid  have  been  added.  In  about  an  hour  (or  later),  during  which  time 
the  pieces  swell  considerably  and  float  from  the  slide,  with  a  clean  needle 
endeavor  to  remove  the  epithelium  ;  it  may  be  loosened  without  much 
trouble  and  floats  off  in  fine  white  shreds.  If  this  is  not  done  cautiously 
the  end-bulbs  lying  close  beneath  the  epithelium  maybe  torn  off  with  it. 
The  more  thoroughly  the  epithelium  is  removed  the  better.  After  the 
pieces  have  lain  four  or  five  hours  in  dilute  acetic  acid  transfer  them 
with  a  few  drops  of  the  same  fluid  to  a  slide,  apply  a  cover-glass 
and  make  slight  pressure  upon  it  with  the  outspread  branches  of  the 
forceps.  On  examination  with  the  low  power  the  blood-vessels  may  be 
distinctly  seen — they  are  recognized  by  their  prominent  nuclei — and  also 
the  medullated  nerve-fibers.*  Trace  such  a  fiber  until  the  medulla  ceases  ; 
examine  such  places  with  the  high  power,  for  there  the  end-bulbs  are 
most  apt  to  be  found.  In  many  cases  nothing  will  be  seen  but  the 
numerous  nuclei  and  even  when  a  favorable  situation  is  found  the  end- 
bulbs  are  so  pale  that  it  is  very  difficult  to  perceive  them  ;  the  axis- 
cylinder,  too,  is  often  very  difficult  to  see  (Fig.  125).  Only  the  prac- 


*  In  the  calf  some  of  the  nerve-fibers  are  nonmedullated  ;  these  are  not  recommended 
for  the  investigation. 


2O6  HISTOLOGY. 

tised  microscopist  will   have  much  success  in  finding  them.      Beginners 
are  advised  not  to  attempt  this  preparation. 

No.  85. — Lamellar  Corpuscles. — These  are  best  obtained  from  the 
mesentery  of  a  cat,  where  they  may  be  seen  with  the  unaided  eye. 
They  appear  as  milky,  glass-like,  transparent,  oval  spots  between  the 
strands  of  adipose  tissue  of  the  mesentery.  Their  number  varies  greatly. 
Occasionally  they  are  very  scarce  and  of  such  small  size  that  to  find 
them  requires  close  searching.  Cut  out  the  portion  of  the  mesentery 
containing  the  corpuscles,  and  spread  them  out  in  a  drop  of  salt  solution 
on  a  slide  lying  on  a  black  background.  Endeavor  to  remove  the 
attached  clusters  of  fat-cells,  taking  care  not  to  prick  the  corpuscles. 
Ascertain  with  a  low  power,  without  a  cover-glass,  whether  the  corpus- 
cles have  been  sufficiently  isolated.  Cover  them  with  another  drop  of 
salt  solution  and  a  cover-glass.  Pressure  must  be  carefully  avoided. 
The  corpuscle  represented  in  Fig.  1 26  was  of  very  small  size. 

With  the  high  power  one  can  distinctly  see  the  nuclei  of  the  cells 
lining  the  capsules  ;  the  oval  nuclei  of  the  inner  bulb  are  often  indistinct 
and  pale.  If  it  is  desired  to  preserve  the  preparation,  treat  it  under  the 
cover-glass  with  I  or  2  drops  of  I  per  cent,  osmic  acid  and,  after  the 
medulla  is  blackened  and  the  inner  bulb  has  become  brown,  displace  the 
acid  with  very  dilute  glycerol.  Methylene-blue  staining  (p.  39)  is  rec- 
ommended. 

No.  86. — Motor  Nerve-endings. — a.  Terminal  Ramifications. — Pre- 
pare a  mixture  of  24  c.c.  of  I  per  cent,  gold  chlorid  solution  plus  6 
c.c.  of  formic  acid,  boil  it  and  let  it  cool  ;  cut  out  small  pieces  3  or  4 
cm.  long  of  the  intercostal  muscles  of  a  rabbit  and  treat  them  like 
No.  82  ;  after  the  dark-violet  pieces  have  lain  from  three  to  six  days  in  70 
per  cent,  alcohol,  tease  a  muscle-bundle  about  5  mm.  broad  in  a  drop 
of  dilute  glycerol  to  which  a  very  small  drop  of  formic  acid  has  been 
added.  It  is  of  advantage  to  make  slight  pressure  on  the  cover-glass. 
To  find  the  terminal  ramifications,  trace  with  the  low  power  the  easily- 
recognized  black  nerve-fibers  (Fig.  128).  The  addition  of  another  drop 
of  acetic  or  formic  acid  often  renders  the  elements  more  distinct. 

b.  Nuclei  of  the  Motor  Plates. — Place  the  anterior  halves  of  the  eye- 
muscles  of  a  recently-killed  rabbit  in  97  c.c.  of  distilled  water  plus  3  c.c. 
of  acetic  acid.  After  six  hours  transfer  the  muscles  to  distilled  water  ; 
with  the  scissors  cut  a  thin  flat  piece  and  spread  it  out  on  a  slide  ;  the 
ramifications  of  the  whitish  nerves  can  be  plainly  seen  with  the  unaided 
eye.  With  low  magnification  (50  diameters),  the  anastomoses  of  the  nerve- 
bundles,  as  well  as  the  blood-vessels,  that  are  easily  recognized  by  the 
transversely-placed  nuclei  of  their  smooth  muscle-fibers,  can  be  seen.  On 
account  of  the  large  number  of  sharply-contoured  nuclei  belonging  to 
the  muscles  and  the  intramuscular  connective  tissue,  the  end-plates  are 
not  easy  to  find.  If  a  nerve-fiber  be  traced  it  will  soon  be  seen  that  the 
double-contoured  medullary  sheath  ceases  abruptly  and  loses  itself  in  a 
group  of  nuclei  ;  these  are  the  nuclei  of  the  motor  plate,  the  other 


THE    PERIPHERAL    NERVOUS    SYSTEM.  2O/ 

details    of  which   are    not  distinctly  visible.     The  cross-striation    of  the 
muscle -fibers,  which  are  very  pale,  is  often  indistinct  (Fig.  129). 

No.  87. — The  Suprarenal  Bodies  ;  Topographical  View. — Fix  the 
entire  suprarenal  body  of  a  child  in  200  c.c.  of  o.  I  per  cent,  chromic 
acid,  and  after  eight  days  harden  it  in  150  c.c.  of  gradually-strengthened 
alcohol  ;  mount  unstained  sections  in  dilute  glycerol  (Fig.  130,  A). 

No.  88. — Elements  of  the  Suprarenal  Body. — Tease  portions  of  the 
fresh  organ  in  a  drop  of  salt  solution.  The  elements  "are  very  delicate 
and  therefore  injured  cells  are  of  frequent  occurrence. 

No.  89. — For  the  study  of  the  minute  structure  of  the  suprarenal 
bodies,  place  2  cm.  cubes  of  the  fresh  organ  in  looc.c.  of  Kleinenberg's 
picrosulphuric  acid  and  after  from  twelve  to  twenty -four  hours  in  an  equal 
quantity  of  gradually-strengthened  alcohol ;  cut  fine  sections,  stain  them 
in  Hansen's  hematoxylin,  and  mount  in  damar  (Fig.  130,  B,  and  Fig. 
131).  For  the  exhibition  of  the  nerves,  treatment  with  the  Golgi  mix- 
ture for  from  six  to  eight  days  and  with  the  0.75  per  cent,  silver  solution 
for  from  two  to  three  days,  or  several  repetitions  of  this  procedure,  is 
recommended. 


V.  THE  DIGESTIVE  ORGANS. 

MUCOUS  MEMBRANES. 

The  inner  surface  of  the  alimentary  tract,  of  the  respiratory  organs, 
of  certain  parts  of  the  genito-urinary  system  and  of  some  of  the  organs  of 
special  sense  are  covered  by  a  soft,  moist  membrane,  the  imtcons  mem- 
brane or  tunica  mucosa.  It  is  composed  of  a  soft  epithelium  and  of 
connective-tissue.  The  latter,  immediately  uruder  the  epithelium,  is 
usuall}j  specialized  and  condensed  to  form  a  structureless  membrane, 
the  membrana  propria  or  basement  membrane  ;  beneath  this  follows  the 
tunica  propria,  which  passes  by  a  gradual  transition  into  the  subjacent, 
loose-textured  tunica  submucosa,  that  in  turn  connects  the  mucous  mem- 
brane with  the  underlying  structures,  for  example,  the  muscles  or  bones. 
The  epithelium  of  the  glands  is  derived  directly  from  the  epithelial  ele- 
ments of  the  mucous  membrane  (see  p.  71). 

THE  Mucous  MEMBRANE  OF  THE  ORAL  CAVITY. 
The  mucous  membrane  of  the  mouth  consists  of  three  parts  :  (i)  the 
epithelium,  (2)  the  tunica  propria,  and  (3)  the  submucosa.  The 
epithelium  is  typical  stratified  squamous  epithelium.  The  tunica  propria 
is  formed  of  interlacing  connective-tissue  bundles  richly  interspersed 
with  elastic  fibers.  The  bundles  of  the  uppermost  strata  are  very  slender 
and  form  a  compact,  apparently  almost  homogeneous  felt-work.  The 
surface  of  the  tunica  propria  is  beset  with  numerous  usually  simple  papillae 
(Fig.  134,  i),  the  height  of  which  varies  greatly  in  the  separate  regions 
of  the  oral  cavity.  The  highest  papillae  (0.5  mm*.)  occur  at  the  edge  of 
the  lips  and  on  the  gums.  The  tunica  propria  passes  without  sharp 
liaoits  into  the  submucosa,  which  consists  of  somewhat  thicker  bundles  of 
connective  tissue,  among  which  the  elastic  fibers  are  not  numerous. 
The  submucosa  is  in  general  loosely  attached  to  the  walls  of  the  oral 
cavity  ;  only  on  the  gums  and  on  the  hard  palate  is  it  firmer  and  here 
intimately  united  to  the  periosteum.  It  contains  the  glands  of  the  mucous 
membrane  ;  these  are,  with  the  exception  of  the  sebaceous  glands  occa- 
sionally found  at  the  edges  of  the  lips,  branched  tubular  mucous  glands 
from  i  to  5  mm.  in  size.  The  main  excretory  duct  (Fig.  134,  2)  is 
somewhat  expanded  at  its  lower  end  and  in  the  great'er  part  of  its  length 

208 


THE    DIGESTIVE    ORGANS. 


209 


is  lined  with  stratified  scaly  epithelium  ;  the  branches  and  twigs  into 
which  it  divides  and  subdivides  are  lined  with  stratified  and  simple 
columnar  epithelium  respectively.  Not  infrequently  the  main  excre- 
tory duct  receives  the  excretory  tubes  of  small  accessory  mucous  glands 
(Fig.  134,  2,  3).  The  minute  structure  of  the  gland-tubules  will  be 
described  with  the  mucous  glands  of  the  tongue.  The  numerous  blood- 
vcsscls  of  the  oral  mucous  membrane  are  arranged  in  two  networks,  situ- 
ated in  two  horizontal  planes,  of  which  the  coarser  lies  in  the  submucosa, 


Epithelium. 


Tunica  propria. 


Submucosa. 


Muscles. 


FIG.  134. — VERTICAL  SECTION  THROUGH  THE  Mucous  MEMBRANE  OF  THE  LIP  OF  ADULT  MAN.  X  30. 
i,  Papilla  ;  2,  excretory  duct ;  the  lumen  is  cut  at  only  one  point ;  3,  accessory  gland  ;  4,  a  branch  of 
the  excretory  duct  in  transverse  section  ;  5,  gland-follicles  grouped  into  lobules  by  connective 
tissue  ;  6,  a  gland-tubule  in  transverse  section.  Techn.  No.  91. 

the  other  finer  in  the  tunica  propria.  From  the  latter  terminal  capillary 
loops  ascend  into  the  papillae.  The  lymph-vessels  similarly  form  two 
networks,  a  coarser  in  the  submucosa,  a  finer  in  .the  tunica  propria.  The 
medullated  nerve-fibers  form  a  wide-meshed  reticulum  in  the  submucosa, 
from  which  many  ramifying  fibers  ascend  to  the  tunica  propria.  Here  they 
terminate  either  in  end-bulbs  or  lose  their  medullary  sheath  and  as  non- 
medullated  nerve-fibers  penetrate  into  the  epithelium,  where  after  repeated 
division  they  terminate  in  free  endings. 

THE  TEETH. 

The  teeth  of  man  and  the  higher  animals  are  solid  structures,  which 
enclose  in  their  interior  a  cavity,  the  pulp-cavity,  filled  with  a  soft  mass, 


210 


HISTOLOGY. 


the  dentinal  pulp.  The  portion  of  the  tooth  within  the  alveolus  or  socket 
is  called  \\\zfang,  the  exposed  portion  the  crown  ;  the  juncture  of  these 
portions  forms  the  neck  ;  the  latter  is  covered  by  the  gums.  The  hard 
substance  of  the  tooth  consists  of  three  different  parts  :  (i)  the  dentine, 
(2)  the  enamel  with  the  enamel  cuticle,  and  (3)  the  ccmcntnm.  The  dis- 
position of  these  parts  is  as  follows  :  the  dentine,  which  contributes  the 
chief  bulk  of  the  tooth  and  determines  its  form,  encloses  the  pulp- 


Enamel.  


Dentine. 


Pulp-cavity. 


\    Crown. 


Cementum.     


FIG.  135. — LONGITUDINAL  SECTION  OF  HUMAN  TOOTH.    X  4.    Techn.  No.  92. 


cavity  except  at  the  apex  of  the  fang  where  a  narrow  nutrient  canal 
admits  the  nerves  and  blood-vessels  to  the  pulp  ;  the  dentine  of  the  crown 
is  covered  by  the  enamel,  of  the  fang  by  the  cementum,  so  that  its  sur- 
face is  nowhere  exposed  (Fig.  135). 

The  dentine  or  ivory  (substantia  eburnea)  is  a  white,  opaque  mass, 
harder  than  bone.  It  consists  of  an  apparently  homogeneous  ground- 
substance  containing  very  fine  fibrillae,  which  is  pierced  by  numerous 


THE    DIGESTIVE    ORGANS. 


21 


minute  channels,  the  dcntinal  tubules.  The  latter  begin  with  a  diameter 
of  about  2.5  IJL  at  the  inner  surface  of  the  dentine,  describe  an  S-shaped 
curve  and  then,  steadily  decreasing  in  caliber,  proceed  in  a  slightly 
wavy  course,  radially  directed  toward  the  outer  surface  of  the  dentine  ; 
there  they  either  terminate  at  the  juncture  of  the  dentine  and  enamel  in 
tapering  ends  or  they  form  a  loop  and  turn  into  a  neighboring  tubule. 
During  their  entire  course  they  send  off  numerous  lateral  branches,  which 
establish  communication  with  neighboring  canaliculi.  The  matrix  imme- 
diately surrounding  the  dentinal  tubules  is  especially  dense  and  forms 
the  so-called  dcntinal  sheaths.  The  lumen  of  the  dcntinal  tubidcs  is 
occupied  by  the  dentinal  fibers.  At  the  peripheral  parts  of  the  dentine 
are  the  interglobular  spaces,  irregular  spaces  varying  in  size  and  filled 


Enamel  prisms. 


Dentine. 


Enamel. 


Dentine. 


Cementum. 


FIG.  136.— FROM  A  LONGITUDINAL  SECTION  OF  THE  LAT- 
ERAL PART  OF  THE  CROWN  OF  A  HUMAN  MOLAR  TOOTH. 
X  240.  i,  Dentinal  tubules,  extending  for  a  short  distance 
into  the  enamel ;  2,  dentinal  globules  projecting  into,  3,  the 
interglobular  spaces.  Techn.  No.  92. 


FIG.  137.— FROM  A  LONGITUDINAL  SEC- 
TION OF  THE  FANG  OF  A  HUMAN 
MOLAR  TOOTH.  X  240.  i,  Dentinal 
tubules  interrupted  by  a  granular  stra- 
tum, with  many,  2,  small  interglobular 
spaces  ;  3,  bone-corpuscles  with  many 
processes.  Techn.  No.  92. 


with  a  soft  mass  ;  into  these  spaces  the  dentine  juts  in  the  form  of  usually 
hemispherical  protuberances,  the  dcntinal  globides  (Fig.  136  and  137). 
At  the  neck  and  in  the  fang  are  many  very  small  interglobular  spaces  ; 
they  form  the  so-cai)ed  granule  stratum  lying  immediately  beneath  the 
cementum. 

The  enamel  (substantia  adamantina)  is  still  harder  than  the  dentine. 
It  is  exclusively  composed  of  long,  hexagonal,  homogeneous  fibers,* 
from  3  to  6  /'•  in  thickness,  the  enamel  prisms  (Fig.  138),  which  are 
firmly  united  with  one  another  by  a  scanty  amount  of  irriguous  cement- 
substance.  They  extend  radially,  with  many  undulations,  from  the  sur- 


The  transverse  bands  do  not  appear  until  after  treatment  with  reagents. 


212 


HISTOLOGY. 


face  of  the  dentine  to  the  free  surface  of  the  enamel  ;  this  is  covered  by 
a  very  thin  but  very  resistant  membrane,  the  enamel  cuticle. 

The  cementum  (substantia  ossea)  coincides  in  its  structure  with  that 
of  bone.  It  contains  many  Sharpey's  fibers.  Haversian  canals  are 
found  only  in  the  cementum  of  older  individuals  ;  stratification  in  lamel- 
lae is  seldom  well  defined.  Bone-corpuscles  are  absent  near  the  neck. 

The  space  between  the  fang  and  the  alveolus  is  occupied  by  the 
richly-innervated  periosteum,  which  is  firmly  united  to  the  cementum 
by  Sharpey's  fibers,  which  penetrate  from  the  inferior  maxilla  through 


Enamel  prisms, 
isolated. 


Enamel  prisms  in  trans- 
verse section. 


Fig.    138.— ENAMEL     PRISMS    FROM   THE 
TOOTH  OF  AN  INFANT.    Techn.  No.  94. 


FIG.  139. — Six  ODONTOBLASTS  WITH  DENTINAL  FIBERS, 
f;  p,  pulp  processes.  From  the  pulp  of  an  infant. 
X  240.  Techn.  No.  93. 


the  periosteum  into  the  cementum.     The  uppermost  portion  of  the  peri- 
osteum is  called  the  circular  dentinal  ligament. 

The  dentinal  pulp  is  formed  of  a  soft  connective  tissue  containing 
delicate  fibers  not  united  in  bundles,  the  cellular  elements  of  which,  on 
the  surface  toward  the  dentine,  form  a  layer  of  elongated  nucleated  cells, 
the  odontoblasts ;  these  send  out  short  processes,  pulp  processes  (Fig. 
139),  that  are  connected  with  other  elements  in  the  pulp,  and  long  pro- 
cesses that  extend  into  the  dentinal  tubules  as  the  above-mentioned 
dentinal  fibers  (Fig.  I39,/).  Blood-vessels  and  nerves  are  limited  to  the 
pulp  of  the  tooth. 

DEVELOPMENT  OF  THE  TEETH. 

The  development  of  the  teeth  in  man  begins  toward  the  close  of  the 
second  month- of  fetal  life  *  and  is  first  indicated  by  a  linear  proliferation 
of  the  primitive  epithelium  of  the  oral  cavity,  which  in  the  form  of  a  con- 
tinuous projection  grows  obliquely  into  the  subjacent  connective  tissue. 


*That  which,  at  an  earlier  period  (fortieth  day),  has  been  described  as  the  anlage,  is  not 
this  alone,  but  includes  the  anlage  of  the  labial  furrow. 


THE    DIGESTIVE    ORGANS. 


213 


This"  projection,  the  dental  ridge  ("enamel   germ")  (Fig.    140,  A)  de- 
velops on  its  lateral  (labial)  surface  knob-like  protuberances,  the  dental 


Epithelium  of  the  margin 
of  the  jaw. 

I 


Dental  bulbs.    Dental  furrow 


Papillae 


Enamel  organs.     C.          Isthmuses.        D 


FIG.  140.— SCHEMATIC  REPRESENTATION  OF  THE  INITIAL  PROCESSES  IN  THE  DEVELOPMENT  OF  THE 
TEETH,  showing  the  formation  of  three  teeth.  The  anlage  of  each  anterior  tooth  is  seen  in  section  ; 
the  cut  surface  is  stippled.  A,  Free  edge  of  the  dental  ridge. 

bulbs  (B),  corresponding  in  number  to  the  temporary  teeth,  while  coin- 
cidently  in  the  surrounding  mesoderm  as  many  conical  aggregations  of 
closely-packed  connective-tissue  cells  arise,  the  young  dental  papilla 


Dental    ridge 
of  upper  jaw. 


I 


I-Q 

Epithelium  of        I>-Q. 
the  oral  cav- 
ity. 


Dental    ridge 
of  lower  jaw. 


Cartilaginous 
nasal  septum. 


Nasal  cavity. 


Anlage  of  the 
upper  jaw. 


Oral  cavity. 


Tongue. 


Anlage  of  the 
lower  jaw. 

FIG.  141.— FRONTAL  SECTION  OF  THE  HEAD  OF  AN  EMBRYO  SHEEP,  4  CM.  LONG.    X  15-    Techn.  No.  95. 


(B)  (tenth  week).  The  latter  advance  obliquely  from  the  labial  side  out 
ot  the  depths  to  the  lingual  side  toward  the  surface  and  are  embraced 
by  the  dental  bulbs  in  such  a  manner  that  these  form  an  epithelial  cap 


214 


HISTOLOGY. 


for  the  dental  papillae.  Thus  each  bulb  becomes  an  enamel  oi'gan. 
Meanwhile  the  dental  ridge  has  assumed  a  more  nearly  vertical  posi- 
tion (C).  At  about  this  time,  too,  a  longitudinal  groove  on  the  margin 
of  the  jaw  is  visible,  the  dental,  furrow,  which  exteriorly  marks  the 
region  from  which  the  dental  ridge  grew  into  the  depths.  The  time  of 
the  appearance  of  the  dental  furrow  varies  ;  frequently  it  is  present  in 
the  initial  stages.  It  disappears  later.  The  original  broad  attachment 
between  the  dental  ridge  and  the  enamel  organ  becomes  diminished  by 
partial  constriction  and  finally  is  reduced  to  a  slender  cord,  the  isthmus 
(Fig.  140,  D).  Meanwhile  the  papilla  and  enamel  organ  grow  beyond 
the  dental  ridge  into  the  depths,  so  that  the  free  edge  of  the  latter  does 


Kpithelium  1 

I   of  oral  mu- 
1-    cous  mem- 
Tunica  I     brane. 
propria  J 


Enamel  or 


Papilla. 


Osseous  trabeculte 
of  lower  jaw. 


Lower  lip. 


Orbicularis  oris  muscle  ii 
transverse  section. 


FIG.   142.—  CROSS-SECTION  OF  THE  LOWER  JAW  OF  A  HUMAN  EMBRYO  FOUR  MONTHS  OLD.      X  42. 

Techn.  No.  95. 

not  extend  to  half  the  length  of  the  enamel  organ  (Fig.  140   and   Fig. 


At  the  same  time  the  elements  of  the  enamel  organ  undergo  differ- 
entiation. The  inner  layer  of  cells,  resting  upon  the  papilla,  develop 
into  tall  columnar  elements,  the  inner  enamel  cells  (Fig.  143);  their  inner 
surface  is  provided  with  a  cuticular  border.  The  peripheral  cells  (Fig. 
143),  steadily  decrease  in  height  (Fig.  144),  until  finally  they  are  reduced 
to  thin  plates,  the  outer  enamel  cells  ;  the  cells  between  the  inner  and  the 
outer  enamel  cells,  by  an  abundant  increase  of  the  intercellular  substance, 
become  transformed  into  stellate,  anastomosing  elements,  and  form  the 
enamel  pulp  (Fig.  143  and  Fig.  144).  At  the  point  where  the  inner 
enamel  cells  bend  over  into  the  layer  of  outer  enamel  cells,  the  enamel 
organ  grows  further  into  the  depths  until  it  has  reached  the  lowest  ex- 


THE    DIGESTIVE    ORGANS. 


215 


tremity  of  the  anlage  of  the  tooth.  Thus  the  enamel  organ,  in  a  measure, 
forms  the  matrix  in  which  the  tooth  develops.  The  determination  of  the 
shape  of  the  future  tooth  is  the  first  function  of  the  enamel  organ  ;  the 
second  is  the  production  of  the  enamel,  which  takes  place  only  in  that 
portion  of  the  layer  of  inner  enamel  cells  enveloping  the  crown  of  the 
tooth.  This  portion  may  be  named  the  enamel  membrane.  Each  cell 
of  this  membrane  deposits  a  substance  which  subsequently  calcifies  and 


Thickened  < 
epithelium  .'. 
of  the  oral  — ~ 

mucous 
membrane. 


Outer  .enamel  cells. 

Enamel  pulp. 
Inner  enamel  cells. 


Free  edge  of  the 
dental  ridge. 

Papilla. 


FIG.  143.— FROM  A  CROSS-SECTION  OF  THE  UPPER  JAW  OF  A  HUMAN  EMBRYO  FIVE  MONTHS  OLD. 

X  42.    Techn.  No.  95. 


becomes  an  enamel  prism.  The  inner  enamel  cells  surrounding  the 
fang  take  no  part  in  the  production  of  the  enamel ;  they  decrease  in 
height  and  (since  here  the  enamel  pulp  soon  disappears)  apply  themselves 
directly  against  the  outer  enamel  cells,  the  two  layers  forming  the 
epithelial  sheath  of  the  fang  (Fig.  144). 

Before  the  production  of  enamel  has  begun  the  first  lamina  of  den- 
tine has 'been  formed  (about  the  twentieth  week).  The  superficial  cells 
of  the  dental  papilla  elongate  and  become  the  odontoblasts,  the  agents 


2l6 


HISTOLOGY. 


which  produce  the  at  first  uncalcified  dentine  (Fig.  144).  The  odonto- 
blasts  do  not  develop  beyond  the  extent  of  the  epithelial  sheath.  As  soon 
as  the  first  dentine  is  formed,  the  epithelial  sheath  undergoes  regressive 


Dental  sack. 
Outer  layer.    Inner  layer. 


Dentine 


Odontoblasts 


Dental  papilla   (future 
pulp). 


Outer  enamel  cells. 


Enamel  pulp. 


'\;V-,       Inner  enamel  cells 
Ef        (enamel  cuticle). 


Enamel. 


Epithelial 

sheath. 


Blood-vessel 
Bony  trabeculae  of  lower  jaw 


FIG.  144. — LONGITUDINAL  SECTION  OF  A  YOUNG  MILK-TOOTH  OF  A  NEWBORN  DOG.    X  42. 

Techn.  No.  95. 


change,  since  connective-tissue  ingrowths  from  the  alveolar  periosteum 
penetrate  between  the  epithelial-cells.  This  regression  begins  at  the 
lower  border  of  the  enamel  organ,  thus  severing  the  connection  between 


THE    DIGESTIVE    ORGANS.  2I/ 

the  latter  and  the  deepest  part  of  the  epithelial  sheath.  With  the  com- 
pleted growth  of  the  tooth  the  last  remnant  of-  the  epithelial  sheath 
disappears. 

Before  the  production  of  enamel  and  dentine  the  connection  between 
the  dental  ridge  and  the  surface  is  severed*  (Fig.  140,  D)  ;  the  meso- 
dermic  tissue  surrounding  the  anlage  of  the  tooth  forms  a  compact 
membrane,  the  dental  sack,  in  which  subsequently  an  inner  looser  and 
an  outer  denser  stratum  can  be  distinguished  (Fig.  144).  The  enamel 
cuticle  and  the  cementum  do  not  appear  until  after  birth,  shortly  before 
the  irruption  of  the  tooth.  The  former  is  produced  by  the  merging  of 
the  cuticular  borders  of  the  enamel  cells  into  a  firm,  homogeneous  mem- 
brane ;  the  latter  is  a  product  of  the  alveolar  periosteum. 

The  permanent  teeth  develop  in  the  same  manner  as  the  temporary 
teeth  ;  in  the  twenty -fourth  week  new  protuberances,  dental  bulbs, 
develop  on  the  edge  of  the  dental  ridge  growing  further  into  the  depths, 
that  embrace  new  papillae  penetrating  from  the  side.  The  anlage  of  the 
permanent  tooth  at  first  lies  in  the  same  alveolus  with  the  temporary  tooth; 
a  separate  alveolus  is  developed  later.  The  completed  tooth  is  in  part  of 
epithelial  origin  (the  enamel),  in  part  derived  from  the  connective -tissue 
dental  papilla  (the  dentine),  the  remains  of  which  persist  in  the  adult  as 
the  dentinal  pulp.  The  cementum  is  in  a  measure  an  accessory  formation 
contributed  by  neighboring  tissues. 

THE  TONGUE. 

The  bulk  of  the  tongue  is  formed  of  striated  muscles,  the  separate 
bundles  and  fibers  of  which  interlace  in  various  directions,  that  for  the 
greater  part  of  their  extent  are  covered  by  a  reflection  of  the  oral 
mucous  membrane.  The  bundles  of  the  muscular  tissue  are  disposed  in 
three  planes  :  (i)  vertically  and  somewhat  radially  (geniohyoglossus, 
lingualis,  and  hyoglossus)  ;  (2)  transversely  (lingualis) ;  and  (3)  longi- 
tudinally (lingualis  and  styloglossus).  Since  the  muscle-bundles  cross 
one  another  for  the  most  part  at  right  angles,  sections  exhibit  a 
beautiful  network.  A  median  septum,  the  septum  lingua,  divides  the 
muscular  tissue  into  a  right  and  a  left  half.  The  septum  begins  low  at 
the  hyoid  bone,  gradually  increases  in  height,  attains  its  greatest 
elevation  in  the  middle  of  the  tongue,  then  gradually  slopes  down 
forward  and  disappears  ;  it  does  not  extend  through  the  entire  half  of 


*The  dental  ridge  has  previously  become  a  perforated  plate,  beset  on  all  sides  with  short, 
jagged  excrescences.  Remains  of  the  dental  ridge  may  be  found  in  the  gums  of  newborn  chil- 
dren and  were  erroneously  regarded  as  glands  (glandulse  tartaricee). 


2  I  8  HISTOLOGY. 

the  tongue,  but  ceases  at  a  distance  of  about  3  mm.  from  the  dorsum  of 
the  organ.  The  septum  is  composed  of  compact  connective  tissue. 

The  mucous  membrane  of  the  tongue,  like  that  of  the  oral  cavity, 
consists  of  an  epithelium,  a  tunica  propria,  and  a  submucosa,  but  is 
characterized  by  the  conspicuous  development  and  complicated  form 
of  the  papillae.  Three  kinds  of  papillae  are  distinguished  :  the  filiform 
or  conical,  \ho,  fungifonn  or  clavate,  and  the  circumvcdlate  papillce. 

The  filiform  papillce  are  cylindrical  or  conical  elevations  of  the  tunica 
propria,  bearing  on  the  summit  from  five  to  twenty  small  secondary 
papillae.  They  are  composed  'of  distinctly-fibrillated  connective-tissue 
and  numerous  elastic  fibers,  covered  by  a  thick  layer  of  stratified  scaly 
epithelium  that  over  the  secondary  papillae  not  infrequently  forms  a 
number  of  filamentous,  horny  processes.  The  filiform  papillae  are  very 


Epithelium.   / 


Epithelium. 


I 


Tunica 
propria 


propria. 

FIG.  145.— LONGITUDINAL  SECTION  OF  THE  Mu-       FIG.  146.— LONGITUDINAL  SECTION  OF  THE  Mu- 
cous MEMBRANE  OF  THE  DORSUM  OF  THE  Hu-  cous  MEMBRANE  OF  HUMAN  TONGUE.     X  3°- 
MAN  TONGUE.     X  30*    i,  Section  of  two  filiform  i,  Fungiform  papilla  with,  2,  secondary  papillae; 
papillae,  each  of  which  bears,  2,  three  secondary            3,  stalk  of   fungiform   papilla;   4,  small  filiform 
papillae  ;    3,    compound,    4,    simple    process    of           papilla.     Techn.  No.  96. 
epithelium,  the  surface  of  which  is  covered  with 
masses  of  loosely-attached,  scaly  epithelial-cells. 
Techn.  No.  96. 

numerous  and  are  distributed  over  the  entire  surface  of  the  tongue  ;  they 
vary  in  height  from  0.7  to  3  mm.  (Fig.  145). 

The  fungiform  papilla  are  rounded  elevations  connected  with  the 
tunica  propria  by  a  slightly-constricted  stalk  ;  their  entire  surface  is 
beset  with  secondary  papillae.  They  consist  of  a  distinct  feltwork  of 
connective-tissue  bundles,  which  contain  but  few  elastic  fibers.  The 
epithelial  cover  is  thinner  than  that  on  the  filiform  papillae  and  is  not 
cor-nified.  The  fungiform  papillae,  not  so  numerous  as  the  filiform,  are 
also  distributed  over  the  entire  surface  of  the  tongue  and  vary  in  height 
from  0.5  to  1.5  mm.  In  the  living  they  are  usually  easily  distinguished  by 
their  red  color,  due  to  the  capillaries  shimmering  through  the  transparent 
epithelium  (Fig.  146). 


THE    DIGESTIVE    ORGANS. 


2I9 


The    circiuircallatc    papilla    resemble    broad,    flattened    fungiform 
papillae  and  are  separated  from  the  surrounding  epithelium  by  a^circular 


Epithelium. 


Tunica  propria. 


Submucosa. 


Secondary  papillae. 


Muscle-fibers. 


FIG.  147. — VERTICAL  SECTION  OF  A  CIRCUMVALLATE  PAPILLA  OF  MAN.     X  30.    Techn.  No.  96. 

furrow  varying  in  depth   and   bounded  by   a  ridge  designated  the  wall. 
The  papillae  are  composed  of  connective  tissue,  like  that  of  the  fungiform 


Epithelium. 


Tunica  propria. 


FIG.  148.— VERTICAL  SECTION  OF  A  LYMPH-FOLLICLE  FROM  THE  ROOT  OF  THE  TONGUE  OF  ADULT  MAN. 
X  20  i.  Crypt  of  the  follicle,  containing  migrated  leucocytes.  2.  Epithelium  of  the  crypt,  infiltrated 
with  leucocytes  on  the  left  and  at  the  base,  almost  intact  on  the  right.  3.  Nodules  of  adenoid  tissue 
containing  germinal  centers  :  /"',  nodules  cut  through  the  middle  ;  /2,  through  the  side  ;  /3,  at  the 
periphery.  4.  Fibrous  sheath.  5.  Section  of  excretory  duct  of  mucous  gland.  6.  Blood-vessel. 
Techn.  No.  96. 

papillae.     Secondary  papillae  are  found   only  on  the  upper,  not  on   the 
lateral  surfaces.      In  the  epithelium  covering  the  sides,  and  occasionally 


220 


HISTOLOGY. 


also  the  wall,  lie  the  end-organs  of  the  gustatory  nerves,  the  taste-buds. 
The  circumvallate  papillae  are  few  in  number,  from  8  to  15,  and  only 
occur  at  the  posterior  end  of  the  dorsum  of  the  tongue.  They  are  from 
I  to  1.5  mm.  high  and  I  to  3  mm.  broad  (Fig.  147).  At  the  lateral 
margins  of  the  tongue,  near  the  anterior  pillars  of  the  fauces,  is  a  group 
of  parallel  folds  of  the  mucous  membrane,  the  papilla  foliata,  that  are 


Emigrating  leucocytes. 


Fragments  of  epithelium. 


Emigrated  leu- ^ 

cocytes. 


L**JK 


«.  )Qs 


Epithelium. 


iJVSf'^  *  • 

:>  «y*  J»  ^  f|» 

-/:  4   C^fi^      '-^•^    H  X®^®' 

^^* 


Adenoid  tissue 
of  the  tunica 
propria. 


*-*7*iS2 


FIG.  149. — FROM  A  THIN  SECTION  OF  A  LINGUAL  FOLLICLE  OF  MAN.  X  420.  On  the  left  the  epithelium  is 
free  from  leucocytes,  on  the  right  many  leucocytes  are  wandering  through.  In  this  way  the  epithe- 
lium is  undermined  and  smaller  or  larger  fragments  of  it  are  seen  lying  between  the  broad  passages 
made  by  the  leucocytes.  Techn.  No.  96. 

distinguished  by  their  wealth  of  taste-buds.  The  papillae  foliatae  are 
especially  well  developed  in  the  rabbit. 

The  submucosa  at  the  tip  and  at  the  edges  of  the  tongue,  is  firm  and 
resistant  (fascia  linguae),  and  intimately  connected  with  the  underlying 
parts. 

The  Lymph-follicles  of  the  Tongue  (folliculi  linguales). — The  mucous 
membrane  of  the  root  of  the  tongue  extending  from  the  circumvallate 


THE    DIGESTIVE    ORGANS.  221 

papillae  to  the  epiglottis  is  peculiarly  modified  by  the  development  of 
lymph-nodules.  They  are  spherical  aggregations  of  adenoid  tissue 
from  i  to  4  mm.  in  size,  that  embedded  in  the  uppermost  strata  of  the 
tunica  propria  form  easily-perceptible  macroscopic  elevations.  In  the 
middle  a  punctate  opening  may  be  seen,  the  entrance  to  a  deep  central 
crypt,  lined  by  a  continuation  of  the  stratified  epithelium  of  the  oral 
mucous  membrane.  Encircling  this  epithelium  is  a  zone  of  diffuse 
adenoid  tissue,  which  contains  a  variable  number  of  lymph-nodules  with 
germinal  centers  and  is  sharply  separated  from  the  fibrillar  connective 
tissue  of  the  tunica  propria  ;  when  the  follicles  are  well  developed,  the 
fibrous  bundles  of  the  tunica  propria  are  circularly  disposed  about  the 
adenoid  tissue  and  so  form  a  fibrous  capsule  (Fig.  148,  4).  Under 
normal  condition's  numerous  leucocytes  of  the  adenoid  tissue  continually 
wander  through  the  epithelium  into  the  central  crypt  and  from  there  to 
the  oral  cavity  ;  they  are  readily  found  in  the  saliva,  as  "mucous  "  and 
"  salivary  "  corpuscles.  The  epithelium  is  often  greatly  expanded  in 
consequence  and  destroyed,  or  is  infiltrated  with  leucocytes  to  such  a 
degree  that  its  boundary  cannot  be  definitely  determined  (Fig.  149). 

The  Glands.  —  Two  kinds  of  branched  tubular  glands  occur  in  the 
mucous  membrane  and*  in  the  superficial  muscular 
strata  of  the  tongue.  The  gland-cells  of  the  one 
kind  produce  a  mucigenous  secretion  (mucin)  ;  they 
are  named  mucous  glands.  The  secretion  of  the 
second  kind  is  a  thin,  watery,  serous  fluid,  distin- 
guished by  the  large  amount  of  albumin  it  contains  ; 
they  are  called  serous  glands. 

The  '  mucous  glands  are  of  the  same  structure 
as  those  of  the   oral  mucous  membrane  and  occur      FIG.  150.—  FROM-A  SECTION 

THROUGH    THE    ROOT   OF 

along  the  edges  and  in  larger  numbers  at  the  root        THE  TONGUE  OF  A 

MOUSE.     X9Q.    A  serous 

of  the   tongue,   where   not   infrequently  their  ex-        gland;  the  tubular  sys- 

J  tern    silvered  by   Golgrs 

cretory  ducts  open  into  the  crypts  of  the  follicles. 


The  ducts  are  lined  by  columnar  epithelium,  which        Cognized,  i 
occasionally  is  ciliated.     The  walls  of  the  tubules 

consist  of  a  structureless  membrana  propria  and  gland-cells  ;  the  latter  are 
columnar  elements  possessing  a  firm  cell-membrane  and  vary  in  appear- 
ance with  their  periodic  functional  state.  The  exhausted  cell  is  smaller, 
the  transverse-oval  nucleus  near  the  base  of  the  cell  (Fig.  151,  /,  £)  ;  the 
cell  loaded  with  secretion  is  broader,  the  nucleus  is  pressed  flat  against 
the  cell-  wall  (Fig.  151,  /,  c,  //).  Generally  the  same  mucous  gland, 
often  the  same  tubule,  exhibits  different  phases  of  secretion  ;  however, 
demilunes  are  not  formed  here,  because  the  rigid  membrane  of  the 


222  HISTOLOGY. 

gland-cells  resists  the  pressure  exerted  by  neighboring  cells.*  The 
anterior  lingual  gland  (glandula  lingualis  anterior}  (Nuhn)  occurring  in 
the  tip  of  the  tongue  also  is  a  mucous  gland. 

The  serous  glands  are  limited  to  the  vicinity  of  the  papillae  circum- 
vallatse  and  foliatae  ;  the  excretory  ducts  open  into v the  furrows  between 
the  papilla  and  the  wall  (Fig.  147),  and  are  lined  by  simple 'or  stratified, 
not  infrequently  ciliated,  columnar  epithelium.  The  small  tubules  con- 
sist of  a  delicate  membrana  propria  and  short  cylindrical  or  conical  cells, 
destitute  of  a  membrane,  the  dim,  granular  protoplasm  of  which  encloses 
a  round  nucleus  lying  in  the  middle  of  the  cell  (Fig.  151,  /Fand  V). 
The  lumen  of  the  tubules,  especially  in  animals,  is  very  narrow. 


FIG.  151. — /,  //.  FROM  A  SECTION  OF  A  Mucous  GLAND  OF  THE  ROOT  OF  A  HUMAN  TONGUE.  7,  Section 
of  a  tubule  with  (b)  gland-cells  empty  of  secretion  and  (c)  gland-cells  filled  with  secretion  ;  d,  lumen. 
//.  Cross-section  of  a  tubule  containing  only  cells  loaded  with  secretion,  ///and  IV.  From  the  mu- 
cous membrane  of  the  tongue  of  a  rabbit.  ///.  Tubule  of  a  mucous  gland  in  transverse  section.  IV. 
Several  tubules  of  a  serous  gland,  at  d  the  very  small  lumen.  V.  Several  tubules  of  a  human  serous 
gland,  with  large  (d1)  and  small  (d)  lumen.  All  the  sections  are  magnified  240  times.  Techn.  No.  96. 

The  blood-vessels  of  the  mucous  membrane  of  the  tongue  form  net- 
works disposed  parallel  to  the  surface,  from  which  twigs  ascend  to  all  the 
papillae  up  into  the  secondary  papillae.  At  the  root  of  the  tongue  small 
arteries  pierce  the  fibrous  envelopes  of  the  lymph-follicles  and  break  up 
into  capillaries  that  penetrate  to  the  interior  of  the  nodules.  The  blood- 
vessels of  the  glands  form  capillary  networks  around  the  glancl-tubules. 

The  lymph-vessels  of  the  tongue  are  arranged  in  two  sets  ;  a  deep  set 
consisting  of  larger  vessels,  and  a  superficial  set,  which  takes  up  the 
lymph-vessels  of  the  papillae.  The  lymph-vessels  at  the  root  of  the 
tongue  are  very  richly  developed  ;  they  form  networks  encircling  the 
lymph-nodules. 

The  nerves  of  the  mucous  membrane  of  the  tongue,  the  glosso- 
pharyngeal  and  the  lingual  branch  of  the  fifth  are  furnished  with  small 
groups  of  ganglion-cells  along  their  course  ;  their  endings  behave  partly 
as  in  other  portions  of  the  oral  mucous  membrane,  partly  they  enter  in 
intimate  relation  with  the  taste -buds. 


*  Only  the  mucous   glands  of  the  tongue  of  the  cat  and  of  the  uvula  of  man  exhibit 
demilunes. 


THE    DIGESTIVE    ORGANS.  223 

THE  PHARYNX. 

The  wall  of  the  pharynx  is  composed  of  three  coats :  a  mucous,  a 
muscular,  and  a  fibrous  coat.  The  mucous  coat,  like  the  oral  mucous 
membrane,  possesses  a  stratified  scaly  epithelium,  a  tunica  propria  beset 
with  papillae,  and  also  numerous  mucous  glands.  The  upper  or  respira- 
tory part  of  the  pharynx  (pars  nasalis)  is  clothed  by  stratified  ciliated 
columnar  epithelium,  the  lower  limit  of  which  is  tolerably  variable.  Very 
richly  developed  is  the  adenoid  tissue.  Between  the  pillars  of  the  fauces 
it  forms  conspicuous  accumulations,  one  on  either  side,  known  as  the 
palatine  tonsils  (tonsilla  palatina),  which  in  respect  to  their  structure  in 
man  and  many  animals  correspond  to  an  aggregation  of  large  lymph  - 
nodules  like  those  of  the  root  of  the  tongue.  The  leucocytes  that  wander 
through  the  epithelium  of  the  tonsils  are  so  numerous  that  the  latter  may 
be  regarded  as  the  most  fertile  source  of  the  salivary  corpuscles.  Many 
mucous  glands  lie  in  the  neighborhood  of  the  tonsils.  The  adenoid 
tissue  is  also  vigorously  developed  in  the  respiratory  portion  of  the 
pharynx,  where  on  the  posterior  wall  between  the  orifices  of  the 
eustachian  tubes  it  forms  a  conspicuous  mass,  the  "  pharyngeal  tonsil," 
which  agrees  in  structure  with  the  palatine  tonsils,  excepting  that  the 
lymphoid  tissue  is  less  sharply  circumscribed.  Here,  too,  many  leuco- 
cytes migrate  through  the  epithelium.  The  development  of  the  adenoid 
tissue  of  the  oral  cavity  and  of  the  pharynx  is  subject  to  considerable 
variation. 

The  muscular  coat  (constrictor  muscles  of  the  pharynx)  consists  of 
striated  muscle-fibers,  the  description  of  which  belongs  to  the  domain  of 
macroscopic  anatomy.  The  fibrous  tunic  is  a  stout  membrane  composed  of 
a  dense  feltwork  of  fibro-elastic  tissue.  Blood-vessels,  lymph-vessels,  and 
nerves  are  distributed  in  the  same  manner  as  in  the  oral  mucous  membrane. 


THE  ESOPHAGUS. 

The  wall  of  the  esophagus  comprises  a  mucous,  a  muscular,  and  a 
fibrous  coat.  The  mucous  coat  is  composed  of  a  stratified  squamous 
epithelium,  of  a  tunica  propria  beset  with  papillae,  following  this  of  a 
stratum  of  longitudinally-disposed  smooth  muscle-fibers,  the  nmscularis 
mucoscz  ;  subjacent  to  the  latter  is  the  submucosa,  which  consists  of  loosely- 
joined  bundles  of  connective  tissue,  which  in  the  upper  half  of  the  esopha- 
gus contains  small  mucous  glands.  The  muscular  tunic,  in  the  upper 
portion  of  the  tube,  is  composed  of  striated  muscle-fibers,  which  in  the 
lower  portion  are  replaced  by  smooth  muscle-fibers.  The  latter  are 


224  HISTOLOGY. 

\ 

arranged  in  two  strata,  an  inner  circular,  in  which  the  direction  of  the 
muscle-fibers  is  not  everywhere  exactly  transverse,  and  an  outer  longi- 
tudinal not  continuous  layer.  The  fibrous  coat  consists  of  compact 
connective-tissue  bundles  interspersed  with  numerous  elastic  fibers. 
The  distribution  of  the  blood-vessels,  lymph-vessels,  and  nerves  is  the 


Mucous  coat. 


Muscular  coat. 


Fibrous  £WM. 


FIG.  152. — FROM  A  CROSS-SECTION  OF  THE  MIDDLE  THIRD  OF  THE  HUMAN  ESOPHAGUS.  X  ic.  i.  Stratified 
squamous  epithelium.  2.  Tunica  propria.  3.  Muscularis  mucosse.  4.  Submucosa.  5.  Circular 
muscles.  6.  Longitudinal  muscles,  g,  Blood-vessel.  Techn.  No.  98. 

same  as  in  the  pharynx.  Between  the  circular  and  the  longitudinal 
layers  of  the  muscular  coat  the  nerves  form  a  plexus,  at  the  nodal  points 
of  which  minute  groups  of  ganglion-cells  occur  (see  plexus  myentericus, 
p.  238). 

THE  STOMACH. 

The  wall  of  the  stomach  is  from  2  to  3  mm.  thick  and  comprises 
three  coats  :  a  mucous,  a  muscular,  and  a  serous  or  fibrous  tunic. 

The  mucous  coat,  sharply  contrasted  with  the  white  esophageal 
mucous  membrane  by  its  reddish-gray  color,  consists  of  an  epithelium, 
a  tunica  propria,  a  muscularis  mucosae,  and  a  submucosa  (Fig.  153). 

The  epithelium  is  a  simple  columnar  epithelium,  the  elements  of 
which  produce  a  mucoid  secretion.  Two  zones  can  usually  be  distin- 
guished, an  upper  mucoid  (Fig.  15,^),  and  a  lower  protoplasmic  (Fig.  I  5 ,  /) ; 
the  latter  contains  the  oval,  round,  or  flattened  nucleus.  The  extent  of 
the  mucoid  zone  varies  considerably  with  the  functional  phase  (cf.  Fig. 
I  5).  After  the  discharge  of  their  mucoid  contents  the  epithelial  elements 
closely  resemble  goblet-cells.  The  tunica  propria  is  corrfposed  of  a 
mixture  of  fibrillar  and  reticular  connective  tissue  and  of  an  extremely 
variable  number  of  leucocytes,  that  occasionally  lie  closely  aggregated 


THE    DIGESTIVE    ORGANS. 


225 


and  form  solitary  lymphatic  nodules.  The  tunica  propria  contains  so 
many  glands  that  its  tissue  is  limited  to  delicate  septa  between  and  to  a 
thin  stratum  below  the  tubules.  In  the  pyloric  end  the  glands  are 
farther  apart,  the  tunica  propria  is  conspicuously  developed  and  not  in- 
frequently elevated  in  filamentous  or  leaf-like  villi. 

Two  kinds  of  gastric  glands  are  recognized :  fundus  glands  * 
(glandulae  gastricae  propriae),  chiefly  situated  in  the  middle  and  cardiac 
thirds  of  the  stomach,  and 
pyloric  glands,  confined  to 
the  narrow  pyloric  region. 
Both  are  simple  tubular 
glands,  often  branched, 
especially  in  the  pyloric 
region,  which  open  singly 
or  in  groups  into  minute, 
pit-like  depressions,  the 
gastric  pits  (foveolae  gas- 
tricae), in  the  mucous 
membrane  of  the  free  sur- 
face. The  portion  of  the 
gland  adjoining  these  de-  Muscuiaris. 
pressions  is  called  the  neck, 
the  following  portion  the 
body,  and  the  blind  end  the 
fundus  (Fig.  154).  Each 
gland  consists  of  a  mem- 
brana  propria  and  of  gland- 
cells. 

The    fundus    glands 

contain  two  kinds  of  cells,  chief-  or  central-cells  and  parietal-  or  acid- 
cells.^  The  former  are  clear,  cubical,  or  short  columnar  cells,  with 
a  granular  protoplasm  surrounding  a  spherical  nucleus.  The  chief- 
cells  are  very  unstable.  The  parietal-cells  are  usually  considerably 
larger,  darker,  and  of  a  rounded  or  triangular  form  ;  their  granular 


Epithelium. 


(   Tunica  propria. 


Muscuiaris 
mucosae. 


Submucosa. 


Inner    circular 
laver  of  muscle. 


Outer  longitud- 
inal layer  of 
muscle. 


Serosa. 


FIG.  153. — TRANSVERSE  SECTION  OF  HUMAN  STOMACH.  X  15. 
The  tunica  propria  contains  glands  standing  so  close  together 
that  its  tissue  is  visible  only  at  the  base  of  the  glands  toward 
the  muscularis  mucosse.  Techn.  No.  oo. 


*  In  the  earlier  text-books  the  fundus  glands  were  called  peptic  glands,  a  name  based 
upon  a  function  of  the  glands  now  called  into  question. 

f  The  assertion  upheld  on  various  sides  that  the  chief-  and  the  parietal-cells  are  different 
functional  appearances  of  one  kind  of  cells,  as  also  the  statement  that  during  digestion  the 
parietal-cells  multiply,  but  disappear  after  prolonged  fasting,  are  very  much  in  need  of  thorough 
investigation.  The  stomach  of  an  animal  killed  after  a  long  winter  hibernation  still  contains 
parietal-cells. 
15 


226  HISTOLOGY. 

protoplasm    surrounds    a    spherical    nucleus.       The    parietal-cells    are 


Epithelium  of  the  surface. 


p 


a 

,B3w 


^  w^iVi 

&      or.;;**,   :1 


I   Gastric  pit. 


if /r  I  f 

\»t—'  ;— s  '        ??H         .       .     , 


Parietal-cells. 


Chief-cells. 


Leucocj'tes. 


Smooth  muscle-fibers. 


Parietal-cell, 


FIG.  154. — VERTICAL  SECTION  OF  THE  Mucous  MEMBRANE  OF  THK  CARDIAC  END  OF  A  HUMAN 
STOMACH.     X   220.     Techn.  No.  102. 


marked    by    their    affinity  for    anilin    dyes,  with   which    they   react  in- 
tensely.    The  two  kinds  of  cells  are  not  equally  distributed  ;  the  chief- 


THE    DIGESTIVE    ORGANS. 


227 


cells  form  the  principal  portion  of  the  gland -fund  us,  the  parietal-cells  are 
irregularly  distributed,  but  are  especially  numerous  in  the  neck  and  the 
body  of  the  tubule.  Here  they  lie  in  rows  beside  the  chief-cells,  but 


Portion  of  a  parietal-cell. 


Parietal-cell  adjoining  a  later; 
branch  of  the  lumen. 


Chief-cell. 


KTT-  Lumen. 


FIG.  155.— TRANSVERSE  SKCTION  OF  A  HUMAN  FUNDUS  GLAND.    X  240.    Techn.  No.  102. 

toward  the  fundus  they  are  pressed  to  the  periphery,  without,  however, 
being  shut  off  from  the  lumen,  with  which  they  communicate  by  a  short 


Tunica  propria, 
with  glands. 


Muscularis 
)     mucosae. 


I 


FIG.  156.— CROSS-SECTION  THROUGH  THE  Mucous  MEMBRANE  OF  THE  FUNDUS  OF  STOMACH  OF  A  MOUSE 
(DURING  DIGESTION).  X  234.  In  the  gland  on  the  right  the  entire  system  of  canaliculi,  in  the  two 
other  glands  only  a  portion  of  the  same,  is  silvered.  The  "  baskets  "  formed  by  the  secretory  capil- 
laries can  be  distinguished.  Techn.  No.  119. 

lateral  canal  extending  between  the  chief-cells  from  the   lumen  to  the 
parietal-cells  (Fig.  155).     This  lateral  canal  is  the  only  one  of  the  system 


228 


HISTOLOGY. 


of  minute  canaliculi  belonging  to  the  parietal-cells  (but  not  to  the  chief- 
cells)  that  can  be  seen  in  ordinary  preparations.  By  the  aid  of  Golgi's 
reaction,  which  also  ''blackens  "  secretion,  it  may  be  seen  that  from  the 


Epithelium  of  the  sur- 
face cut  obliquely,  so 
that  it  appears  to  be 
stratified. 


•';:$*: -.^v?::' 


•Tunica  propria. 


- — Pylonc  gland. 


Portions  of  pyloric 
glands. 


Solitary  follicle. 


Muscularis  mucosa?. 


FIG.  157. — VERTICAL  SECTION  OF  THE  HUMAN  PYLORIC  Mucous  MEMBRANE.     X  90.     Techn.  No.  102  b. 

axial  or  chief  lumen  of  the  fundus  glands  transverse  canaliculi  emerge, 
that  divide  and  either  terminate  in  free  branches  or  anastomose  with  one 
another  and  form  a  narrow-meshed  network  of  "secretory  capillaries," 
that  surrounds  each  parietal-cell  like  a  basket  or  spreads  out  within  the 


THE    DIGESTIVE    ORGANS.  2 29 

cell  itself.  (Fig.  19  and  Fig.  156.)  The  secretion  discharged  from  all 
sides  of  the  cell  passes  into  the  secretory  capillaries,  then  into  one  or 
more  short  lateral  canals,  and  finally  into  the  lumen  of  the  gland. 

The  pyloric  glands  are  furnished  almost  throughout  with  columnar 
cells*  containing  a  spherical  nucleus  situated  near  the  base  of  the  cell, 
which  in  the  intermediate  zone,  that  is,  the  border  zone  between  the  pyloric 
and  the  fundus  mucous  membrane,  very  closely  resemble  the  chief-cells, 
to  which  they  have  been  compared. 

The  foregoing  description  applies  to  the  stomach  as  it  appears  when 
fasting  ;  during  digestion  the  parietal -cells  are  larger,  the  chief-cells,  as 
well  as  the  cells  of  the  pyloric  glands,  are  darker,  the  nuclei  of  the  latter 
are  pushed  nearer  to  the  middle  of  the  cell,  and  the  secretory  capillaries 
expanded  with  increased  contents  are  wider  than  in  the  fasting  organ. 

The  muscularis  mucosce  consists  of  smooth  muscle-fibers  arranged  in 
two  or  three  layers  superposed  in  different  directions,  from  which  single 
strands  branch  off  and  ascend  vertically  between  the  gland-tubules  (Fig. 

154). 

The  submucosa  is  composed  of  loosely-united  connective-tissue  bun- 
dles and  elastic  fibers  and  occasionally  contains  small  clusters  of  fat-cells. 
The  muscular  coat :  it  is  only  in  the  pyloric  region  that  two  separate 
layers  of  smooth  muscle-fibers  can  be  distinguished,  a  thicker  inner  circu- 
lar and  a  thinner  outer  longitudinal  layer.  In  the  other  regions  of  the 
stomach  the  arrangement  of  the  muscle-tissue  is  very  complicated  owing 
to  the  extension  of  the  muscular  strata  of  the  esophagus  to  the  stomach, 
as  well  as  to  the  curving  of  the  organ  that  ensues  in  the  course  of  develop- 
ment ;  sections  exhibit  bundles  of  fibers  extending  in  every  possible 
direction  (Fig.  153). 

The  serous  coat  will  be  described  with  the  peritoneum. 

For  the  vessels  and  nerves  see  p.  236  and  p.  238. 


THE  INTESTINES. 

The  wall  of  the  intestines,  like  that  of  the  stomach,  is  composed 
of  three  tunics,  a  mucous,  a  muscular,  and  a  serous. 

The  mucosa  is  thrown  into  circular  folds,  the  valvulae  conniventes, 
well  marked  in  the  upper  part  of  the  small  intestine,  the  object  of  which 
is  to  increase  the  superficial  extent  of  the  membrane.  In  addition  to 
these  readily  perceptible  plications  there  are  still  other  contrivances 


*  In  man  isolated  parietal-cells  are  found  ;   in  animals,  e. ,?'.,  the  dog,  a  few  dark  conical 
cells  occur,  that  owe  their  appearance  to  the  compression  exerted  by  neighboring  cells. 


230 


HISTOLOGY. 


serving  a  similar  purpose,  that  stand. at  the  limit  of  macroscopic  percep- 
tion. These  are  the  minute  elevations  and  depressions  of  the  mucous 
membrane.  The  former,  the  villi,  are  present  only  in  the  small  intestine, 
in  the  large  intestine  of  man  they  are  wanting  ;  they  are  processes  about 
one  mm.  high,  in  the  duodenum  of  leaf-like,  in  the  remainder  of  the  small 
intestine  of  cylindrical  form.  The  depressions  begin  at  the  pylorus  and 
are  found  throughout  the  whole  length  of  the  intestine.  They  exist  in 
their  most  primitive  form  in  fishes  and  originate  in  longitudinal  parallel 


Epithe- 
lium. 


Tunica 
propria. 


Submucosa.  -~ 


Circular  muscula 

layer. 

Longitudinal  mus 
cular  layer. 


FIG.  158.— LONGITUDINAL  SECTION  OF  THE  JEJUNUM  OF  ADULT  MAN.  X  16.  The  circular  fold 
(valvula  conniventis)  on  the  right  supports  two  small  solitary  nodules,  that  do  not  extend  into  the 
submucosa  and  of  which  the  left  exhibits  a  germinal  center,  X.  The  epithelium  is  slightly  loosened 
from  the  connective-tissue  core  of  many  of  the  villi,  so  that  a  clear  space,  XX,  exists  between  the  two. 
The  isolated  bodies  lying  near  the  villi  (more  numerous  to  the  left  of  the  valvulse  conniventes)  are 
partial  sections  of  villi  that  were  bent,  therefore  not  cut  through  their  entire  length.  Techn.  No.  105. 

folds  of  the  mucous  membrane  connected  by  small  transverse  folds.  In 
vertical'  sections  these  shallow  depressions  appear  as  short,  wide  sacks, 
called  cjypts.  In  mammals  the  crypts  are  deeper,  their  lumen  narrower, 
and  in  rows  close  beside  one  another  they  have  the  appearance  of  simple 
tubular  glands  ;  but  they  could  only  be  regarded  as  such  if  the  epithelial- 
cells  lining  them  produced  a  specific  secretion,  which  is  not  the  case. 
However,  the  name  intestinal  glands  (Lieberkiihn)  has  been  retained. 
Whether  the  isolated  granular  cells  that  occur  in  the  fund  us  of  the  crypts 
are  gland-cells,  is  a  question. 


THE    DIGESTIVE    ORGANS. 


231 


The  mucous  membrane  consists  of  an  epithelium,  a  tunica  propria, 
a  muscularis  mucosae,  and  a  submucosa.     The  epithelium,  which  clothes 


Tangential  sections        Artefacts, 
of  villi.      - 


Epithelium... 


Muscularis 
mucosae. 


Submucosa.    --' 


Intestinal  glands. 


Oblique  sections  of  intestinal  glands. 


FIG.  159. — SECTION  OF  THE  Mucous  MEMBRANE  OF  THE  JEJUNUM  OF  ADULT  MAN.  X  80.  The  empty 
space,  a,  between  the  tunica  propria  and  the  epithelium  ol  the  yilli  is  an  artificial  product,  the  result  of 
the  shrinking  action  of  the  fixing  fluid.  Not  infrequently  within  the  space  lie  cells  that  have  been 
pressed  out  of  the  tunica  propria.  In  its  retraction  the  epithelium  often  tears  and  then  the  ^villus 
appears  to  have  an  opening,  b,  at  its  apex.  The  goblet-cells  have  been  drawn  on  one  side  of  the 
villus  to  the  right.  Techn.  No.  105. 


FIG.  160. — SECTION  OF  THE  Mucous  MEMBRANE  OF  THE  LARGE  INTESTINE  OF  ADULT  MAN,  SHOWING. 

THE   INTESTINAL  GLANDS  (CRYPTS  OF  LlEBERKUHN).      X  8o.      (Schapef.)      Techn.  No.  1OS. 

the  entire  free  surface,  envelopes  the  villi  and  lines  the  crypts,  is  a  simple 
columnar  epithelium,  the   elements  of  which  in  their  mature  condition 


232  HISTOLOGY. 

consist  of  a  granular  protoplasm  containing  numerous  resorbed  fat- 
particles,  a  usually  oval  nucleus,  and  a  cell-membrane.  On  the  free  sur- 
face of  the  cells  there  is  a  sometimes  homogeneous,  sometimes  finely- 
striated  cuticular  border  characteristic  of  the  intestinal  epithelium. 

The  regeneration  of  the  epithelium  takes  place  only  in  the  intestinal 
crypts,  where  by  mitotic  division  new  cells  are  constantly  formed, 
which  gradually  move  upward  and  replace  the  cells  that  disintegrate  on 
the  upper  surface  of  the  mucous  membrane.  Therefore  the  youngest 
generation  of  epithelial-cells  is  found  in  the  crypts,  the  oldest  on  the  free 
upper  surface,  in  the  small  intestine  on  the  apices  of  the  villi.  Goblet- 
cells  in  extremely  variable  numbers  occur  in  the  intestinal  epithelium  ; 
they  possess  an  elliptical,  not  infrequently  a  chalice-like  form  ;  the  upper 
portion,  that  directed  toward  the  surface  of  the  intestine,  undergoes 
different  degrees  of  distention  as  the  protoplasm  is  transformed  into 
mucus,  the  nucleus  with  the  remainder  of  the  unaltered  protoplasm  lies 


FIG.  161. — INTESTINAL  EPITHELIUM.  X  560.  A.  Isolated  goblet-cells  of  rabbit,  x,  Escaping  mucus. 
Techn.  No.  104  b.  B.  From  a  section  of  the  mucous  membrane  of  the  human  intestine,  b,  A  goblet- 
cell  between  columnar  cells.  Techn.  No.  102. 

at  the  base  of  the  cell ;  a  cuticular  border  is  wanting,  in  place  of  which 
a  sharply-defined  circular  orifice  is  found,  through  which  the  mucus  is 
poured  out  on  the  surface  (Fig.  161,  A).  The  goblet-cells  are  derived 
from  the  ordinary  epithelial-cells  of  the  intestine.  In  proper  conditions 
each  young  intestinal  epithelial-cell  may  assume  the  functions  of  a  goblet- 
cell.* 

The  separate  phases  of  secretion  appear  in  regular  sequence  and  so 
that  the  later  phases  are  always  to  be  seen  on  the  apices  of  the  villi  or  near 
the  upper  surface  of  the  mucous  membrane,  the  initial  phases  in  the 
intestinal  crypts  (Fig.  162). 

In  the  crypts  of  the  small  intestine  the  number  of  goblet-cells  is 
proportionately  less  than  in  the  large  intestine  ;  this  is  explained  by  the 
fact  that  the  young  epithelial-cells  of  the  crypts  move  more  rapidly  to  the 

*  In  regard  to  the  mode  in  which  the  goblet-cells  produce  and  discharge  secretion,  see  p.  69. 


THE    DIGESTIVE    ORGANS. 


233 


surface,  the  greater  superficies  of  the  small  intestine,  so  much  increased 
by  the  villi,  necessitating  a  greater  supply  of  young  cells  to  replace  those 
that  disintegrate  on  the  surface  ;  the  elaboration  of  mucus  often  does  not 
take  place  in  the  crypts,  but  first  begins  in  the  cells  on  the  villi.  In  the 
large  intestine,  where  the  villi  are  absent,  the  passage  to  the  surface  takes 
place  slowly  and  the  cells  have  time  to  produce  secretion  during  their 
sojourn  in  the  crypts.  Out  of  this  arose  the  misconception  that  the  crypts 


Epithelium. 


Tunica  propria. 


' Portion  of  a  capillary 

blood-vessel. 


Basal  border. 

Nucleus  of  a  wandering 
leucocyte. 


Tangential  section  of  a 
goblet-cell. 


Mucoid  zone  of  a  gob- 
let-cell. 


Nucleus  of  a  smooth  muscle-fiber. 


Lacteal  or  chyle-vessel. 


FIG,  162.— LONGITUDINAL  SECTION  THROUGH  THE  APEX  OF  THE  VILLUS  OF  A  DOG.    X  360-    The  goblet- 
cells  contain  the  less  mucus  the  nearer  they  lie  to  the  summit  of  the  villus.     Techn.  No.  106. 


of  the  small  intestine  produced  a  serous  fluid  ;  those  of  the  large  intestine 
a  mucoid  secretion. 

Between  the  epithelial-cells  migratory  leucocytes  from  the  underlying 
tunica  propria  are  found  in  varying  numbers. 

The  tunica  propria  chiefly  consists  of  fibrillar  arid  reticular  connec- 
tive tissue  that  contains  an  extremely  variable  number  of  leucocytes. 
O \ving  to  the  numerous  crypts  present  the  tunica  propria  of  the  large 
intestine  is  confined  to  the  spaces  between  and  to  a  narrow  zone  below 
the  tubules,  as  in  the  stomach  ;  throughout  the  small  intestine  the  tunica 
propria  extends  into  the  villi. 


234 


HISTOLOGY. 


The  muscularis  inncosa  consists  of  an  inner  circular  and  an  outer 
longitudinal  layer  of  smooth  muscle-fibers.  Fibers  derived  from  the 
muscularis  mucosae  extend  within  each  villus  nearly  to  its  apex.  Their 
contraction  effects  a  shortening  of  the  villus  (cf.  Techn.  No.  105). 


Intestinal  crypts. 
Duodenal  glands. 


Ganglion-cells  of  Auerbach's  — - 
plexus. 


Epithelium.   • 
Tunica  propria. 

Muscularis  mucosse  - 
Submucosa. 


Circular  muscular 
layer. 


Longitudinal  mus- 
cular layer 


Mucosa. 


Muscularis. 


FIG.  163. — LONGITUDINAL  SECTION  THROUGH  THE  DUODENUM  OF  A  CAT.  X  30.  The  epithelium  has 
become  loosened  from  the  connective  tissue  of  the  villus  on  the  extreme  left.  The  two  villi  at  the 
extreme  right  are  cut  obliquely.  The  epithelium  has  fallen  from  the  middle  villus,  so  that  the  con- 
nective-tissue core  lies  exposed.  The  serosa  is  represented  by  a  line  beneath  the  longitudinal  layer 
of  the  muscular  coat.  Techn.  No.  103. 

The  submucosa  consists  of  loose  fibrous  connective  tissue  and  in  the 
upper  half  of  the  duodenum  contains  branched  simple  tubular  glands, 
the  duodenal  glands  (Brunner),  from  0.2  to  3.4  mm.  in  size.  The 
excretory  ducts  of  these  glands  are  clothed  with  columnar  cells,  pierce 
the  muscularis  mucosae,  and  run  in  the  tunica  propria  parallel  with  the 
crypts  of  Lieberkiihn.  The  walls  of  the  tubules  are  formed  of  columnar 
gland-cells  and  a  structureless  membrana  propria. 

THE  LYMPH-NODULES. 

It  has  been  previously  mentioned  that  the  tunica  propria  of  the 
mucous  membrane  contains  leucocytes  or  lymphoid-cells  in  variable 
numbers,  occurring  either  as  diffuse  adenoid  tissue  or  as  circumscribed 
masses  from  0.5  to  2  mm.  in  size.  The  latter  are  lymph-nodules,  which 
occur  either  singly  as  the  solitary  nodules  or  in  groups  as  the  agminatcd 
nodules. 

The  solitary  nodules  ("  solitary  follicles")  vary  greatly  in  number 
in  the  gastric  mucous  membrane,  they  are  more  numerous  in  the  intes- 


THE    DIGESTIVE    ORGANS. 


235 


tines.  They  usually  possess  an  oval  form  and  in  the  beginning  of  their 
development  always  lie  in  the  tunica  propria,  close  under  the  epithelium, 
with  their  base  directed  toward  the  muscularis  mucosae.  With  advancing 
growth  (in  cats  at  birth)  they  break  through  the  muscularis  mucosae 
and  expand  in  the  submucosa,  where  the  loose  tissue  offers  but  little 
resistance.  The  part  of  the  nodule  lying  in  the  submucosa  has  a 
spherical  outline  and  soon  becomes  considerably  larger  than  that  within 
the  tunica  propria.  The  completed  solitary  nodules,  therefore,  are  in 
general  pear-shaped,  with  the  small  end  turned  toward  the  epithelium. 


Villi. 


itestinal  glands.    . 


Submucosa. 


Longitudinal 
layer 


Of  muscularis. 


FIG.  164.— TRANSVERSE  SECTION  OF  A  PATCH  OF  PEYER  OF  THE  SMALL  INTESTINE  OF  A  CAT. 
crests  of  four  nodules  were  not  within  the  plane  of  the  section.     X  10.    Techn.  No.  107. 


The 


Where  the  nodules  are  situated  the  villi  are  wanting  and  the  crypts  are 
pushed  aside.  The  solitary  nodules  are  composed  of  adenoid  tissue  and 
usually  contain  a  germinal  center.  The  young  leucocytes  formed  in 
them  in  part  pass  into  the  neighboring  lymph-vessels  and  in  part 
wander  through  the  epithelium  into  the  intestine.  The  columnar 
epithelium  covering  the  apex  of  the  nodules  contains  wandering  leuco- 
cytes (Fig.  165). 

The  agminatcd  nodules  (patches  of  Peyer)  are  groups  of  from  ten  to 
sixty  nodules  that  lie  side  by  side,  never  over  one  another,  each  of  which 


236  HISTOLOGY. 

has  the  structure  of  a  solitary  nodule.  Occasionally  the  outline  of  an 
individual  nodule  is  altered  by  the  pressure  of  adjacent  nodules  (Fig. 
164).  They  principally  occur  in  the  lower  portion  of  the  small  intestine, 
either  isolated  from  one  another  or  transformed  in  a  mass  of  diffuse 
adenoid  tissue,  in  which  case  only  the  germinal  centers  can  be  distin- 
guished. This  is  not  infrequently  the  case  in  the  vermiform  process  of 
man.  The  transition  of  the  mucous  membrane  of  the  rectum,  character- 
ized by  the  large  intestinal  crypts,  into  that  of  the  anal  canal  occurs  at  the 


Epithelium. 


Tunica  propria. 


FIG.  165.— FROM  A  SECTION  OF  THE  SMALL  INTESTINE  OF  A  SEVEN-DA  VS'-OLD  KITTEN.  X  250.  Crest 
of  a  solitary  follicle.  The  epithelium  on  the  left  contains  many  wandering  leucocytes.  The  epithelium 
on  the  right  contains  but  three  leucocytes.  Techn.  No.  107. 

upper  end  of  the  columnae  rectales  (Morgagni) ;  the  crypts  cease  and 
instead  of  the  simple  cylindrical  epithelium  a  thick,  stratified  squamous 
epithelium  appears,  which  covers  papillae  containing  blood-vessels. 

The  muscular  layer  of  the  intestine  consists  of  an  inner  robust 
circular  and  an  outer  thinner  longitudinal  stratum  of  smooth  muscle- 
fibers.  In  the  large  intestine  the  longitudinal  muscular  layer  is  well 
developed  only  at  the  folds  corresponding  to  the  intervals  between  the 
sacculi ;  between  these  folds  it  is  extremely  thin. 

The  structure  of  the  serosa  will  be  described  with  the  peritoneum 
(p.  254). 

THE  BLOOD-VESSELS  OF  THE  STOMACH  AND  OF  THE  INTESTINES. 

The  blood-vessels  of  the  stomach  and  of  the  large  intestine  have  a 
precisely  similar  distribution,  which  is  modified  in  the  small  intestine  by 
the  presence  of  the  villi.  In  the  stomach  and  in  the  large  intestine  the 
entering  arteries  first  give  off  small  branches  to  the  serosa,  then  pierce 
the  muscularis,  which  they  supply,  and  then  in  the  submucosa  form  a 
network  extending  parallel  to  the  surface.  From  this  small  twigs  ascend 
through  the  muscularis  mucosae  and  in  the  tunica  propria  at  the  base  of 
the  glands  form  another  network  parallel  to  the  surface.  Fine  capillaries 
(from  4.5  to  9  //.  wide)  arise  from  the  latter,  which  form  plexuses  around 
the  glands  and  pass  into  wider  capillaries  (from  9  to  18  /'-),  which  latter 


THE    DIGESTIVE    ORGANS. 


237 


form  a  subepithelial  plexus,  that  wreath-like  lies  about  the  mouths  of  the 
glands.  Venules  take  their  origin  from  the  wide  capillaries,  pass  vertically 
down  between  the  gland-tubules  and  open  into  a  venous  plexus  lying 
parallel  to  the  surface  in  the  tunica  propria  ;  in  their  further  course  the 
veins  run  alongside  the  arteries.  The  veins  arising  from  the  venous 
plexus  in  the  subrhucosa  are  furnished  with  valves  to  the  point  where  they 
open  into  the  collecting  veins  approaching  the  intestine  along  parallel 
paths.  The  remaining  branches  and  the  trunk  of  the  portal  vein  are 
without  valves. 

Lymph-follicle. 


Tunica  propria. 


_.    Submucosa. 

Circular  muscles. 
Longitudinal  muscles 


Vein. 


Artery. 


FIG.  166.— FROM  A  CROSS-SECTION  OF  THE  INJECTED  SMALL  INTESTINE  OF  A  RABBIT.  X  50.  The  lymph- 
nodule  is  sectioned  so  that  in  the  upper  half  the  superficial  capillary  network  is  visible,  in  the  lower 
half,  the  capillary  loops  occurring  within  the  interior  of  the  nodule.  The  section  is  thick  and 
unstained,  and  the  crypts  of  Lieberkiihn  cannot  be  distinguished,  i.  The  network  of  blood-vessels 
within  the  muscularis;  2,  within  the  submucosa;  3,  within  the  tunica  propria.  Techn.  No.  no. 

In  the  small  intestine  only  the  arteries  supplying  the  crypts  are  dis- 
tributed in  the  same  manner  as  in  the  large  intestine.  The  villi  are 
provided  with  one  artery  (several  when  the  villi  are  broad),  which  lies 
opposite  the  vein  ;  from  the  former  capillaries  arise  that  lie  close  under 
the  epithelium  and,  obliquely  or  vertically  to  the  long  axis  of  the  villus, 
pass  into  the  veins.*  The  further  course  of  the  veins  is  the  same  as  in 
the  large  intestine. 


*  The  distribution  is  the  same  in  the  dog,  but  in  the  rabbit  and  the  guinea-pig  the  arteries 
going  to  the  villi  break  up  into  fine  branches  that  run  to  the  base  of  the  villus  and  then  form  a 
capillary  network  that  lies  close  under  the  epithelium  (Fig.  166,  a).  At  the  summit  of  the 
villus  the  capillaries  open  into  a  small  venous  trunk  that  in  the  course  of  its  vertical  descent 
takes  up  the  capillaries  surrounding  the  mouths  of  the  glands  (Fig.  166,  7'). 


238  HISTOLOGY. 

The  duodenal  glands  are  enveloped  in  a  capillary  plexus  supplied 
by  the  blood-vessels  of  the  submucosa. 

The  lymph-nodules  are  surrounded  by  a  superficial  capillary  network, 
from  which  fine  capillaries  extend  into  the  interior  ;  often  these  do  not 
penetrate  to  the  center,  which  is  then  without  blood-vessels  (Fig.  166). 

THE  LYMPH-VESSELS  OF  THE  STOMACH  AND  OF  THE  INTESTINES. 

The  lymph-  (chyle)  vessels  of  the  stomach  and  of  the  large  intestine 
begin  in  the  mucous  membrane  as  blind  capillaries,  about  30  p.  wide,  and 
descend  between  the  gland-follicles.  In  the  mucous  membrane  of  the 
small  intestine  the  lymph-vessels  begin  in  the  axis  of  the  villi ;  in  cylin- 
drical villi  they  are  simple  (in  leaf-shaped  villi  multiple)  canals  (from  27 
to  36  fj.  wide)  closed  at  their  upper  ends,  the  lymph-radicles  or  lacteals. 
All  these  vessels  descend  to  a  narrow-meshed  capillary  plexus  lying  at 
the  base  of  the  glands  and  extending  parallel  to  the  surface,  which  com- 
municates by  numerous  anastomoses  with  a  wide-meshed  horizontal 
plexus  in  the  submucosa  ;  the  lymph-vessels  proceeding  from  this  network 
are  provided  with  valves  ;  they  penetrate  the  muscular  coat  and  take  up 
the  vessels  of  a  plexus  lying  between  the  circular  and  the  longitudinal 
muscular  strata,  called  the  intramuscular  lymphatic  plexus,  which  takes 
up  the  numerous  lymph  capillaries  of  both  muscular  layers.  The  vessels 
then  run  beneath  the  serosa  to  the  mesentery  and  pass  onward  between 
its  folds. 

In  certain  localities  the  course  of  the  lymph-vessels  in  the  mucosa 
is  modified.  The  nodules  of  the  patches  of  Peyer  never  contain  lymph- 
vessels.  They  press  aside  the  capillaries,  which  run  in  the  interstices 
between  them,  constantly  decreasing  in  number  but  increasing  in  caliber. 
It  is  probable  that  the  lymph-sinuses  of  the  rabbit  (p.  125,  remark)  are 
nothing  else  than  such  immensely -widened,  flattened  capillaries. 

THE  NERVES  OF  THE  STOMACH  AND  OF  THE  INTESTINES. 
The  numerous  nerves,  mainly  consisting  of  gray  fibers,  form  a  plexus 
beneath  the  serosa,  then  pierce  the  longitudinal  layer  of  the  muscular 
tunic  and  between  this  and  the  circular  layer  are  arranged  in  a  conspicu- 
ous network,  the  intramuscular  ganglionic  plexus  {plexus  myentericus) 
(Auerbach)  ;  numerous  groups  *  of  multipolar  ganglion -eel  Is  are  found 
along  the  course  of  the  nerves,  usually  at  the  nodal  points  of  the  net- 
work, the  meshes  of  which  are  angular  or  elliptical.  From  this  network- 
bundles  of  gray  fibers  are  given  off  usually  at  right  angles,  that  in  part 

*  The  groups — small  ganglia — behave  like  the  sympathetic  ganglia  in  general. 


THE    DIGESTIVE    ORGANS. 


239 


supply  the  longitudinal  and  circular  strata  of  the  muscular  tunic,  while 
another  portion  pierces  the  latter  and  enters  the  submucosa.  In  the 
muscular  coat  the  nerves  form  a  rich  rectangular-meshed  network,  from 
which  nerve-fibers  turn  aside  and  after  repeated  division  approach  the 
muscle-fibers,  on  which  (not  within)  they  terminate  in  free  club-shaped 
endings.  The  nerves  in  the  submucosa  form  a  delicate  plexus,  the  plexus 
sitbmucosus  (Meissner),  the  meshes  of  which  are  narrower  and  groups  of 


A  B 

FIG.  167.— A.  SURFACE  VIEW  OF  THE  PLEXUS  MYENTERICUS  OF  AN  INFANT.  X  50.  g,  Groups  of 
ganglion-cells;  r,  layer  of  circular  muscle-fibers,  recognized  by  their  rod-shaped  nuclei.  Techu.  No. 
i ii  a. 

B.  SURFACE  VIEW  OF  THE  PLEXUS  SUBMUCOSUS  OF  THE  SAME  INFANT.  X  .so.  g,  Groups  of  ganglion- 
cells;  b,  blood-vessel  shimmering  through  the  overlying  tissue.  Techn.  No.  in  b. 

ganglion-cells  smaller.  From  this  spring  numerous  fibers  which  enter 
the  tunica  propria  and  in  part  weave  a  nervous  net  about  the  glands, 
in  part  enter  the  villi,  where  they  terminate  free  in  the  parenchyma  or 
close  beneath  the  epithelium,  without  connection  with  the  epithelial-cells.* 
A  network*  corresponding  to  the  intramuscular  ganglionic  plexus 
also  occurs  between  the  layers  of  the  muscular  coat  of  the  esophagus. 


THE  SALIVARY  GLANDS. 

The  salivary  glands  are  the  submaxillary,  sublingual,  and  parotid 
glands,  and  the  pancreas.  They  are  compound  tubular  glands,  which 

*  Spindle-shaped  or  stellate  elements  have  been  described  as  nerve  cells  of  the  intestinal 
plexuses,  the  processes  of  which  form  a  plexus  surrounding  the  blood-  and  lymph-vessels. 
They  do  not  stand  in  any  relation  to  the  above-described  plexuses,  nor  can  any  nerve-processes 
be  distinguished  on  them,  so  that  their  nature  is  still  uncertain. 


240 


HISTOLOGY. 


l> 


elaborate  either  a  mucous  or  a  richly-albuminous  serous  fluid,  or  both 
the  mucous  and  the  serous  secretion.  Accordingly  we  distinguish  :  (i) 
mucous  salivary  glands  (sublingual  in  man,  the  rabbit,  dog,  and  cat  ; 
submaxillary  in  the  dog  and  cat)  ;  (2)  serous  salivary  glands  (the  parotid 
in  man,  the  rabbit,  dog,  and  cat  ;  submaxillary  in  the  rabbit,  and  the 

pancreas)  ;  (3)  mixed  salivary  glands 
(submaxillary  in  man,  the  ape,  guinea- 
pig,  and  mouse). 

TJie  Sublingual  Gland. — The  excre- 
tory duct,  ductus  sublingualis  (Bartholin), 
consists  of  a  two-layered  cylindrical  epi- 
thelium and  fibre-elastic  tissue.  It  is 
continued  as  the  intralobular  or  mucous 
tubes,  the  low 'columnar  epithelium  of 
which  exhibits  the  characteristic  striation 
(Fig.  170,  A)  only  in  a  few  places.  In- 
tercalated tubules  cannot  be  demon- 
strated with  certainty,  it  is  much  more 
probable  that  the  mucous  tubes  pass 
directly  into  the  terminal  compartments. 
The  latter  are  composed  of  a  membrana 
propria  and  of  mucous  cells.  The 
membrana  propria  is  formed  by  stellate 
connective  -  tissue  cells  ;  the  empty 
glandular  cells  occur  in  groups,  the 
"  demilunes  "  therefore  appear  very  large 

(Fig.  168,  I,  2).  The  connective -tissue  between  the  tubules  and  the 
lobules  is  rich  in  leucocytes. 

The  Parotid  Gland. — The  excretory  duct,  ductus  parotideus  (Stenon), 
is  distinguished  by  its  broad,  compact  membrana  propria  close  beneath 
the  epithelium,  but  otherwise  is  like  that  of  the  sublingual  gland.  It 
divides  and  passes  into  the  in  tralobular  tubes,  the  columnar  cells  of  which 
at  the  base  exhibit  distinct  vertical  striation.  Following  these  are  the 
intercalated  tubules,  which  are  lined  by  elongated,  often  spindle-shaped, 
cells.  The  intercalated  tubules  continue  to  the  terminal  compartments, 
which  consist  of  a  delicate  membrana  propria  with  stellate  connective- 
tissue  cells  and  of  cubical  serous  glandular  cells.  In  a  state  of  exhaus- 
tion the  cells  are  small,  dark,  and  granular ;  in  a  state  of  activity 
they  appear  larger  and  somewhat  clearer. 

The  Submaxillary  Gland. — The  excretory  duct,  ductus  submaxillaris 
(Wharton),  likewise  possesses  a  two-layered  columnar  epithelium,  a 


FIG.  168.— FROM  A  THIN  CROSS-SECTION 
OF  HUMAN  SUBLINGUAL  GLAND.  X  240. 
Of  the  seven  tubules  represented,  only 
three  (i,  2,  3)  are  sectioned  so  as  to  be 
suitable  for  study.  In  2  are  six  cells 
loaded  with  secretion  (s.g}  ;  and  two 
empty  cells  (s.l)  are  crowded  to  the  per- 
iphery, where  they  form  a  "  crescent."  In 
3  all  the  cells  are  filled  with  secretion, 
and  have  deeply-stained  contents ;  4, 
tangential  section  of  a  similar  tubule. 
5,  6,  7,  oblique  sections  of  tubules  like  i 
and  2,  which  show  the  crescents,  but  not 
the  lumen  of  the  gland,  mp,  Membrana 
propria.  £,  Connective  tissue  with  nu- 
merous leucocytes,  ^.  Techn.  No.  112. 


THE    DIGESTIVE    ORGANS. 


24I 


connective-tissue  layer  rich  in  cells,  and  outside  of  this  a  thin  stratum 
of  longitudinally-disposed  muscle-fibers  ;  it  continues  as  the  intralobular 
tubes  lined  with  characteristic  epithelium*  (Fig.  170,  A),  which  pass  into 


FIG.  169.— FROM  A  THIN  SEC- 
TION OF  HUMAN  PAROTID 
GLAND.  X  240.  j,  Interca- 
lated tubule;  the  outlines  of 
the  cells  cannot  be  distin- 
guished. The  very  narrow 
lumen  of  the  gland-tubule  is 
seen  only  at  //  the  remain- 
ing gland-tubules  are  cut  ob- 
liquely. Techn.  No.  112. 


FIG.  170. — FROM  A  THIN  SECTION  OF  HUMAN  SUBMAXILLARY 
GLAND.  X  240.  A.  Cross-section  of  a  salivary  tube  ;  the  epithelial 
cells  on  the  right  are  partially  loosened  from  the  surrounding  con- 
nective tissue,  b;  on  the  same  side  the  striation  in  the  outer  zone 
of  the  cells  is  best  seen  ;  £,  nuclei-of  wandering  leucocytes;  s,  secre- 
tion. B.  Tubules  (m)  with  mucous  gland-cells  showing  four 
lumina ;  <?,  tubules  with  serous  gland-cells  showing  one  lumen  ; 
b,  blood-vessels,  of  which  the  lowermost  is  cut  longitudinally  and 
contains  colored  blood-corpuscles.  Techn.  No.  112. 


the  short  intercalated  tubules  clothed  with  cubical  cells.  The  latter  lead 
into  the  end-pieces,  which  are  clothed  either  with  serous  gland-cells  (as 
in  the  parotid)  or  with  mucous  gland-cells  and  demilunes. 

The  Pancreas. — The  excretory  ducts,  dnctns  pancreaticus  (Wirsung) 


B 


_  Terminal  compartment  (tangen- 

;?*.-•      &~  A  tf  ^Hw^fi^J*1  •  JW  •*  7      *      "  tiol    co*-»t  \r\*i  \ 


tial  section). 


Intercalated  tubule  (longitudinal 
section). 


End-piece  (halved). 
Intercalated    tubule    (transverse 
section). 

End-piece  (halved). 


Intercalated  tubule. 

FIG.  ryi.— A.  GLAND-CELLS  FROM  THE  PANCREAS  OF  A  CAT.  X  560.  Above,  groups  of  cells  as  they 
usually  appear ;  below,  two  isolated  cells.  B.  FROM  A  CROSS-SECTION  OF  THE  PANCREAS  OF  AN 
INFANT.  X  240.  Techn.  No.  113. 


and  ductus  pancreaticus  accessorius  (Santorini),  are  formed  of  a  simple 
columnar  epithelium  and  of  fibrous  connective  tissue,  which  latter  is 
denser  beneath  the  epithelium,  looser  toward  the  periphery.  The  walls 


*  It  contains  a  yellow  pigment,  that  is  visible  in  preparations  fixed  with  alcohol. 
16 


242 


HISTOLOGY. 


of  the  main  excretory  duct  and  its  larger  branches  contain  minute  mucous 
glands.  Intralobular  tubes  with  their  characteristic  epithelium  are 
wanting.  The  branches  of  the  excretory  duct  continue  directly  into 

the  intercalated  divisions  ;  the  columnar 
epithelial-cells  of  the  former  steadily 
diminish  in  height  and  eventually  pass 
over  into  the  flattened  cells,  placed  par- 
allel to  the  long  axis,  of  the  intercalated 
tubules.  These  tubules  are  very  long 
and  narrow  ;  toward  the  end-pieces  they 
divide  and  then  abruptly  terminate  at  the 
epithelium  of  the  terminal  pieces.*  This 
epithelium  consists  of  short  cylindrical 
or  conical  cells,  which  are  characterized 
by  the  highly-refracting  granules — 
"  zymogen  granules  "  f — occupying  the 
zone  adjoining  the  lumen  and  are  thus 
distinguished  from  all  other  glandular  cells  (Fig.  171,  A,  and  Fig.  172). 
The  clearer  peripheral  zone  of  the  cell  contains  the  round  nucleus.  The 
granular  and  clear  divisions  of  the  cell  vary  in  proportionate  extent  with 


^ 


FIG.  172. — TRANSVERSE  SECTION  OF  A 
GLAND-TUBULE  OF  THE  PANCREAS  OF 
NECTURUS  ;  showing  zymogen  granules. 
X  4<x).—(Schaper.) 


- — / Central  lumen. 


Intercellular 
secretory 
capillary. 

FIG.  173.— FROM  A  SECTION  OF  THE  PANCREAS  OF 
ADULT  MAN.  X  320.  Techn.  No.  119. 


Crescent. 


Intercellular 
secretory 
capillary. 


FIG.  174.— FROM  A  SECTION  OF  THE  SUBMAXIL- 
LARY  GLAND  OF  A  DOG.  X  320.  Techn. 
No.  119. 


the  functional  state  of  the  cell.      In  the  beginning  of  digestion  the  gran- 
ules disappear  and  the  clear  belt  becomes  deeper.      Subsequently  the 


*  Continuations  of  the  epithelium  of  the  intercalated  tubules  into  the  interior  of  the 
terminal  pieces  form  the  so-called  "  centroacinal  cells,"  which  as  squamous  elements  lie  upon 
the  inner  surface  of  the  epithelial-cells  of  the  end-pieces. 

f  These  granules  are  not  artefacts,  "as  are  so  many  other  granules  in  cells,  which  are 
produced  by  fixatiort  in  sublimate  or  nitric  acid.  The  zymogen  granules  can  be  seen  in  the  cells 
of  the  fresh  pancreas. 


THE    DIGESTIVE    ORGANS.  243 

granular  zone  increases  to  such  an  extent  that  it  occupies  nearly  the 
whole  of  the  cell.  In  a  fasting  state  the  two  zones  are  of  equal  size. 

In  glands  treated  by  the  method  of  Golgi,  the  secretion  often  stains 
and  the  duct-system  in  its  entire  extent  appears  black.  The  secretory 
capillaries  going  from  the  central  lumen  of  the  terminal  compartments 
may  then  be  seen  (Fig.  173  and  174)  running  between  the  gland-cells; 
they  do  not  quite  reach  to  the  membrana  propria  and  without  anastomoses 
terminate  in  free  branches.  Their  terminal  ends  possibly  lie  within  the 
gland-cells  (cf.  p.  74). 

The  blood-vessels  of  the  salivary  glands  are  very  richly  developed. 
The  arterial  stems,  as  a  rule,  run  along  side  the  main  excretory  duct,  where 
they  divide  into  numerous  branches  which  pass  between  the  lobules  and 
finally  penetrate  within  the  latter,  break  up  into  capillaries  and  form  close 
networks  around  the  tubules.  The  capillaries  lie  in  immediate  proximity 
to  the  gland-cells.  The  larger  veins  follow  the  course  of  the  arteries. 

With  regard  to  the  lymph-vessels  little  is  known  with  certainty.  The 
interfascicular  clefts  between  the  lobules  and  the  tubules  have  been  de- 
scribed as  lymph-channels. 

The  salivary  glands  are  profusely  supplied  with  plexuses  of  medul- 
lated  and  nonmedullated  nerves,  along  the  course  of  which  microscopic 
groups  of  ganglion-cells  occur.  The  fine  nonmedullated  nerve-fibers 
partly  ramify  in  the  walls  of  the  blood-vessels,  partly  form  an  "epilem- 
mal "  plexus  lying  immediately  upon  the  membrana  propria  of  the 
gland-tubules  ;  from  this  delicate  filaments  arise  which  pierce  the  mem- 
brana propria  and  as  hypolemmal  fibers  terminate  in  short,  varicose, 
simple  or  branched  ends,  which  lie  upon  the  gland-cells.* 


THE  LIVER. 

The  liver  is  a  compound  tubular  gland.  On  making  an  incision 
into  a  liver  or  on  examining  its  outer  surface,  it  will  be  observed  that  it 
is  divided  into  irregular  polygonal  areas,  well  defined,  as  in  the  hog,  or 
poorly  defined,  as  in  man  and  the  majority  of  mammals.  These  areas 
are  the  lobules  of  the  liver  (incorrectly  named  acini).  Their  real  form  is 
somewhat  like  that  of  a  prism  with  a  rounded  upper  end  and  a  trans- 
versely-blunted base  (Fig.  175).  They  are  2  mm.  high  and  I  mm.  broad. 
Close  under  the  capsule  of  the  liver  the  lobules  often  are  arranged  with 
their  apex  looking  toward  the  surface  and  a  section  made  parallel  to 
the  surface  will  pass  through  the  lobules  transversely  (Fig.  177)  ;  in  the 

*  In  other  glands  (coil  glands,  mammary  glands,  tarsal  glands)  the  relations  are  the   same. 


244 


HISTOLOGY. 


-—     Interlobular  vei 


-^-'-    Central  vein. 


Cords  of  hepatic 
cells  (trabecuke)- 


interior  of  the  liver  the  lobules  stand  in  different  directions.  Each, lobule 
consists  of  gland-cells  and  blood-vessels  and  is  separated  from  neighbor- 
ing lobules  by  the  interlobular  connective  tissue,  which  supports  the 
branches  of  the  excretory  duct  (the  hepatic  duct),  the  branches  of  the 
portal  vein  and  the  hepatic  artery,  the  lymph-vessels  and  the  nerves. 

The  demarcation  of  the  lobules  de- 
pends on  the  development  of  the 
interlobular  connective  tissue. 

The  main  excretory  duct,  the 
hepatic  duct,  and  its  larger  branches 
consist  of  a  single  stratum  of  columnar 
epithelium,  occasionally  containing 
goblet-cells,  and  of  fibrous  connective 
tissue  separated  into  tunica  propria 
and  submucosa.  The  tunica  propria 
is  the  carrier  of  the  glands  of  the  bile- 
duct,  chiefly  short,  pear-shaped  folli- 
cles lined  with  mucous  gland-cells, 
and  of  isolated  longitudinally-  and 
transversely-disposed  plain  muscle- 
fibers.  The  cystic  duct,  the  ductus 
clwledocJius,  and  the  gall-bladder  ex- 
hibit the  same  structure  ;  the  tunica 

propria  is  elevated  into  minute  anastomosing  rugae  and  the  mucosa  is 
supplemented  by  a  thin  layer  of  interlacing  smooth  muscle-fibers.  The 
columnar  epithelial-cells  of  the  gall-bladder  are  distinguished  by  their 
height  (0.05  mm.)  from  those  of  the  ductus  choledochus  (0.024  mm.).* 
The  branches  arising  from  the  further  division  of  the  hepatic  duct,  the 
interlobular  bile-ducts,  exhibit  thinner  walls  as  they  diminish  in  caliber  ; 
the  larger  consist  of  simple  columnar  epithelium  and  fibro-  elastic  tissue, 
the  smallest  possess  only  a  structureless  membrana  propria  and  a  simple 
layer  of  low  epithelial-cells  provided  with  a  cuticular  border,  which  as 
they  enter  at  the  margin  of  the  lobules  annex  themselves  directly  to  the 
true  glandular  cells.  This  transition  is  very  difficult  to  see  and  can  be 
distinctly  perceived  only  in  sections  in  which  the  bile-ducts  have  been 
injected  or  blackened  by  Golgi's  silver  method. 

The  glandular  cells  of  the  liver,  the  hepatic  cells,  are  irregular  poly- 


FIG.  175.— SCHEME  OF  AN  HEPATIC  LOBULE, 
represented  in  transverse  section  below  and, 
by  partial  leveling,  in  longitudinal  section 
above.  In  the  left  half  the  blood-vessels  are 
drawn ;  in  the  right  half  only  the  cords  of 
hepatic  cells.  X  20. 


*  The  vasa  aberrantia,  or  blind  bile-ducts,  that  chiefly  occur  at  the  left  border  of  the  liver, 
at  the  portal  fissure,  and  in  the  neighborhood  of  the  vena  cava,  are  embryonal  remains  of  liver 
substance  and  do  not  occur  in  the  parenchyma  of  the  organ. 


THE    DIGESTIVE    ORGANS. 


245 


heclral  elements  consisting  of  a  granular  protoplasm  and  of  one  or  more 
nuclei ;  they  have  no  cell-membrane.  The  protoplasm  contains  granules 
of  pigment  and  globules  of  fat  of  various  sizes,  which  latter  are  invariably 
found  in  mammalian  animals  and  well-nourished  persons.  The  cells 


FIG.  176. — LIVER-CELLS  OF  MAN.     X  560.    A.  Isolated  liver-cells  containing  smaller  and  larger  fat-drops, 

.     f ;  b,  imprint  from  contact  with  a  blood-vesfiel.     Techn.  No.  114. 
B.  From  a  section  :  i,  exhausted  cells;  2,  active-cells,  filled  with  secretion.    Techn.  No.  116. 

vary  in  size  from  18  to  26  tu.  The  appearance  of  the  liver-cells  depends, 
as  in  other  gland-cells,  on  the  phase  of  functional  activity.  In  a  fasting 
condition  they  are  small,  dim,  and  have  indistinct  contours  ;  during 
digestion  they  are  larger,  have  a  clear  center,  and  at  the  periphery  a 


Central  veins. •( 


Branch  of  portal  vein. 

Larger  interlobular  bile-duct. 


Interlobular  connective 
tissue. 


Central  vein. 


FIG.  177.— FROM  A  HORIZONTAL  SECTION  OF  HUMAN  LIVER.  X  40.  Three  central  veins,  cut  trans- 
versely, represent  each  a  center  of  as  many  hepatic  lobules,  that  at  the  periphery  are  but  slightly 
defined  from  their  neighbors.  Below  and  to  the  right  of  the  section  the  lobules  are  cut  obliquely  and 
their  boundaries  cannot  be  distinguished.  Techn.  No.  116. 

coarsely-granular  zone.       In    man   the   two    states   are   frequently  ex- 
hibited in  the  same  liver  (Fig.  176,  B). 

In  the  lower  vertebrates  (amphibians  and  reptiles)  the  hepatic  cells 
form  typical  tubes,  but  in  the  higher  vertebrates  their  arrangement  is  a 


246 


HISTOLOGY. 


very  peculiar  one  and  not  a  trace  of  tubular  structure  is  to  be  seen,  as 
might  be  presupposed  from  the  tubular  character  of  the  liver.  The  cells 
are  united  in  small  trabeculae  or  cords,  the  so-called  cords  of  liver-cells, 
that  radially  disposed  around  a  small  vein  (the  central  vein)  situated  in  the 
axis  of  the  lobule  spread  out  toward  the  periphery  (Fig.  175  and  Fig.  1 77), 
and  by  lateral  branches  anastomose  with  neighboring  cords  of  cells.  A 
lumen  cannot  be  distinguished  in  such  cords  by  the  usual  methods  ;  it 
can  only  be  successfully  shown  by  injecting  the  system  of  canals  from 
the  hepatic  duct  or  by  employing  Golgi's  method,  which  blackens  the 


Branch  of  portal 
vein. 


Small  interlobular 
bile-duct,  continu- 
ing into  bile-capil- 
laries. 


Large    interlobular 
bile-duct. 


Branch    of   hepatic 
artery. 


Bile-capillaries. 


Boundary,  toward  the  central  vein. 

FIG.  178. — TRANSVERSE  SECTION  OF  THE  LIVER  OF  A  DOG.     X  240.     Bile-capillaries  blackened  according 
to  the  method  of  Golgi.     Techn.  No.  119. 

bile.  In  such  preparations  it  may  be  seen  that  the  canal-system  (lumen) 
of  the  minutest  interlobular  bile-ducts  is  continued  directly  into  the 
lobules  and  there  apparently  forms  a  network  with  polygonal  meshes. 
In  reality  there  are  but  few  true  meshes  ;  the  network  is  simulated  by 
the  zigzag  course  of  the  bile-canaliculi  and  the  crossing  in  different  planes 
of  the  blind  lateral  twigs  with  which  they  are  furnished  (Fig.  178). 

The  ramifications  of  the  entire  intralobular  system  of  canaliculi 
appear  to  have  little  relation  to  the  branching  of  the  cords  of  hepatic 
cells.  The  latter  branch  much  less  than  the  former  and  thus,  apparently, 


THE    DIGESTIVE    ORGANS. 


247 


the  intralobular  canaliculi  have  attained  a  certain  degree  of  independence, 
as  implied  in  the  name  bile-  capillaries,  bestowed  upon  them.  This  also 
accounts  for  the  hitherto  always  fruitless  endeavor  to  demonstrate  a 
special  wall  for  the  bile-capillaries.  There  can  be  no  wall  other  than 
that  formed  by  a  modification  of  the  exoplasm  of  that  side  of  the  hepatic 
cells  where  the  furrow  for  the  bile-capillary  is  situated  ;  this  stratum  of 
the  cell  protoplasm  is  continuous  with  the  cuticular  border  of  the  epithe- 
lial-cells of  the  interlobular  bile-ducts  (p.  244). 

Thin  sections  clearly  show  that  the  bile-capillaries  stand  in  the  same 
relation  to  the  hepatic  cells  as  the  lumina  of  other  glands  to  the  sur- 
rounding gland-cells,  at  least  in  the  main.  But  nevertheless  certain 
differences  exist.  The  first  difference  is  this,  that  only  a  few,  usually 
two  hepatic  cells  suffice  to  bound  the  bile-capillaries,  while  in  other 
glands  the  lumen  is  bounded  by  several  cells  (Fig.  184).  The  explanation 
of  this  may  be  found  in  the  conspicuous  difference  between  the  diameter 
of  the  lumen  (the  bile-capillary) 
and  that  of  the  hepatic  cell  ;  two 
cells  are  sufficient  to  completely 
surround  the  lumen.  Hence  the 
capillary  is  formed  by  the  appo- 
sition of  the  furrow-like  depres- 

sions Of  tWO  COntigUOUS    hepatic 

cells  (Fig.  185). 

A  second  difference  consists 
herein,  that  a  distinction  between 
main  lumen  and  secretory  capil- 

laries, such  as  can  be  made  in  many  glands,  is  impossible  ;  one  cannot 
say  :  the  hepatic  cells  present  one  surface  to  the  main  lumen,  the  other 
surfaces  to  the  secretory  capillaries,  one  can  only  say,  that  the  liver-cells 
present  several  surfaces  to  the  bile-capillaries.  This  fact  renders  intelli- 
gible the  luxuriant  ramification  of  the  latter,  despite  the  fact  that  relatively 
few  cells  are  required  to  circumscribe  them.* 

Of  the  blood-vessels  of  the  liver,  the  portal  vein  assumes  the  role 
that  falls  to  the  artery  in  other  glands,  while  to  the  hepatic  artery  is 
assigned  the  subordinate  part  of  the  maintenance  of  the  interlobular 


Bile-capillaries  with- 
out lateral  twigs. 


FlG-      .- 


Bile-capillaries  with 
lateral  twigs. 


DOG. 


*  Not  infrequently  it  may  be  seen  that  short  fine  lateral  twigs  leave  the  bile-capillaries 
and  terminate  in  a  minute  knob-shaped  end.  The  knob  corresponds  to  a  small  vacuole  in  the 
liver-cell,  which  communicates  with  the  bile-capillary  by  means  of  a  delicate  canal,  the  minute 
lateral  twig.  These  undoubtedly  are  transient  formations  occurring  in  connection  with  certain 
functional  phases  ;  the  proof  of  this  I  detect  therein  that  entire  areas  of  the  system  of  canaliculi 
may  be  free  from  these  knobs,  while  close  beside  every  capillary  is  beset  with  them  (Fig.  179). 


248 


HISTOLOGY. 


branches    of  the    bile-ducts,    of  the    portal    vein,    and    of  the    hepatic 
veins. 

From  the  branches  of  the  portal  vein,  that  because  they  run  in  the 
interlobular  connective  tissue  are  called  interlobnlar  veins,  spring  numer- 
ous capillaries  possessing  a  width  of  from  10  to  14  /JL.  They  penetrate 
within  the  lobules,  repeatedly  anastomose  with  one  another  during  their 
course,  and  finally  empty  into  a  small  vein  lying  in  the  axis  of  the  lobule, 
the  central  vein  (intralobnlar  vein\  visible  in  transverse  and  longitudinal 
sections  even  of  the  uninjected  liver  (Fig.  177).  The  central  veins  rep- 
resent the  radicles  of  the  hepatic  veins  and  empty  into  the  sublolntlar 


Venae  interlobulares. 

Venae  intralobulares  (centrales). 

Vena  interlobularis 

-»-&&m& 


FIG.  180.-  HORIZONTAL  SECTION  OF  THE  LIVER  OF 
A  RABBIT.  Injected  through  the  portal  vein. 
X  40.  Three  hepatic  lobules  are  represented. 
The  injection  mass  filled  only  the  branches  of  the 
portal  vein  (interlobular  veins) ;  in  the  upper  lob- 
ule it  penetrated  to  the  central  vein.  Techn. 
No.  118. 


FIG.  181. — HORIZONTAL  SECTION  OF  THE  LIVER  OF 
A  CAT.  Injected  through  the  vena  cava  inferior. 
X  40.  Four  hepatic  lobules  are  shown.  The 
injection  mass  filled  the  central  vein  and  the  cap- 
illaries emptying  into  it,  but  did  not  penetrate  to 
the  interlobular  veins.  Techn.  No.  118. 


veins,  which  run   along  the  slightly-flattened  side,  the  so-called  base,  of 
the  hepatic  lobules  (Fig.  182). 

The  relation  between  the  portal-capillaries  on  the  one  side  and  the 
hepatic  cells  and  the  bile-capillaries  on  the  other  calls  for  especial  con- 
sideration. Between  the  meshes  of  the  portal  capillary  network  the 
cords  of  hepatic  cells  are  inserted,  consequently  the  relation  of  blood- 
vessels and  gland-cells  is  a  very  intimate  one ;  sections  show  that  a 
hepatic  cell  is  in  contact  with  capillaries,  not  only  on  one  but  on  several 
sides  (Fig.  183).  This  is  a  unique  phenomenon,  that  does  not  occur  in 


THE    DIGESTIVE    ORGANS. 


249 


other  glands,  where  the  blood-vessels  touch  the  cells  only  on  one 
surface,  and  is  only  comprehensible  when  we  recall  that  in  cross-sections 
the  lumen  (bile-capillary)  is  bounded  by  only  two  cells,  while  in  other 


Hepatic  lobules. 


Interlobular  connec- 

live  tissue. 


Central  (intralobular) 
veins. 


Sublobular  vein. 


FIG.  182. — FROM  A  VERTICAL  SECTION  OF  THE  LIVER  OF  A  CAT. — Injected  through  the  vena  cava 
inferior.  A  sublobular  vein  cut  longitudinally;  it  takes  up  the  central  veins.  The  greater  part  of 
the  injection  mass  has  fallen  out  of  the  wide  blood-vessels.  X  15.  Techn.  No.  118. 

tubular  glands  the  lumen  in  cross-section  is  bounded  by  six  or  more 
cells  (Fig.  184).  But  as  in  other  glands,  so  also  in  the  liver,  the  gland- 
cells  are  inserted  between  the  lumen  on  the  one  hand  and  the  blood- 


Blood-capillaries. 


Bile-capillaries.  -^ 


Hepatic  cells.  * 


FIG.  183. — FROM  A  SECTION  OF  THE  LIVER  OF  A  RABBIT.  X  240.  The  portal  capillaries  were  injected 
with  a  red  mass,  the  bile  capillaries  with  a  blue  mass.  The  hepatic  cells  are  in  contact  with  blood- 
capillaries  on  both  sides.  At  a  few  points  the  red  mass  has  retracted  and  given  rise  to  a  space  (/) 
between  the  hepatic  cells  and  portal-capillaries.  The  bile-capillaries  are  nowhere  in  contact  with 
portal-capillaries,  but  are  always  separated  from  them  by  half  the  breadth  of  a  cell.  The  dark 
spots  on  the  portal-capillaries  are  optical  cross-sections  of  blood-capillaries  which  run  vertically  to 
the  plane  of  the  section. 

vessels  on  the  other.      Nowhere  do  blood-capillaries  and  bile-capillaries 
lie  close  beside  one  another  ;  they  are  always  separated  by  a  gland-cell 

The  most  convincing  demon- 


or  by  an  intervening  portion  of  the  same. 


250 


HISTOLOGY. 


stration  of  this  is  afforded  by  thin  sections  of  rabbit's  liver  in  which  the 
blood-vessels  have  been  transversely  cut  (Fig.  185);  these  also  plainly 
show  that  the  bile-capillaries  run  along  the  surfaces,  the  vascular  capil- 


Gland-lumen. -%-Tr. 


Gland-lumen    (bile-capil- 
larv). 


FlG.  184.— SCHEMK  OF  AN  ORDINARY  GLAND-TUBULE   (LEFT)   AND   OF   A   HEPATIC-TUBULE  (RIGHT). 

laries  at  the  corners  of  the  hepatic  cells  ;  however,  this  is  not  invariably 
the  case,  the  bile-capillaries  sometimes  run  along  the  .edges,  a  behavior 
that  occurs  in  particular  in  man  (Fig.  185,  X). 


Hepatic  cell. 


Bile- 
capillary. 


Blood-  '- 
capillaries. 


FIG.  185.— THIN  SECTION  OF  THE  LIVER  OF  A  RABBIT,  WITH 
INJECTED  BILE-CAPILLARIES.  X  560.  (The  drawing  is  not 
schematic.)  Two  of  the  hepatic  cells  are  in  contact  with 
four  blood-capillaries  (i,  2,  3,  4).  X.  Bile-capillary  at  the 
edge  of  a  hepatic  cell. 


FIG.  186.— FROM  A  SHAKEN  SECTION  OF 
HUMAN  LIVER.  X  240.  c,  Blood- 
capillaries,  at  x  still  containing  blood- 
corpuscles,  b,  Interlobular  connec- 
tive tissue.  On  the  right  are  five 
hepatic  cells;  the  others  have  fallen 
"out  of  the  meshes  of  the  capillary 
network.  Techn.  No.  117. 


The  branches  of  the  hepatic  artery  follow  the  course  of  those  of  the 
portal  vein  and  ramify  only  in  the  interlobular  tissue,  where  they  form 
capillary  networks  about  the  larger  bile-ducts  and  the  branches  of  the 


THE    DIGESTIVE    ORGANS.  25! 

portal  and  the  hepatic  veins.  The  capillaries  proceeding  from  the  artery 
open  into  the  portal  interlobular  veins  or  into  the  portal-capillaries  at 
the  margin  of  the  lobules.  In  the  capsule  of  the  liver  the  hepatic  artery 
forms  a  wide-meshed  capillary  plexus. 

The  course  of  the  blood-vessels  therefore  is  as  follows  :  the  portal 
vein  enters  at  the  transverse  fissure,  repeatedly  divides  into  branches 
that  steadily  decrease  in  size  and  run  in  the  connective  tissue  between 
the  lobules  as  the  interlobular  veins.  From  these  capillaries  arise,  which 
pass  toward  the  axis  of  the  lobule  and  terminate  in  the  central  vein. 
Several  of  the  latter  unite  in  the  formation  of  each  of  the  sublobular 
veins,  which,  like  the  larger  hepatic  veins  they  form  by  their  union,  run 
between  the  lobules. 

The  liver  is  provided  with  a  capsule  consisting  of  fibro-elastic  tissue, 
capsula  fibrosa  (Glisson),  which  is  especially  well  developed  at  the 
transverse  fissure  and  in  the  form  of  special  sheaths  for  the  different 
channels  *  penetrates  into  the  interior  of  the  liver,  where  it  is  usually 
found  in  such  small  amount  between  the  lobules  that  the  boundaries  of 
the  latter  are  very  imperfectly  defined.  Delicate  fibers  ("  lattice  fibers  ") 
derived  from  the  interlobular  connective  tissue  penetrate  into  the  interior 
of  the  lobules,  where  for  the  most  part  they  are  arranged  in  the  form  of 
a  delicate,  radially-placed  latticework. 

The  lymph-vessels  accompany  the  branches  of  the  portal  vein,  which 
netlike  they  embrace  ;  with  the  portal-capillaries  they  enter  the  interior 
of  the  hepatic  lobules,  which,  having  arrived  at  the  central  vein,  they 
then  abandon.  These  deep  lymphatics  communicate  with  a  superficial 
narrow-meshed  network  of  lymph-vessels  which  occurs  in  the  capsule 
of  the  liver. 

The  nerves  chiefly  consist  of  nonmedullated  nerve-fibers,  with  which 
only  a  few  medullated  nerve-fibers  are  mingled  ;  they  enter  the  interior  ot 
the  liver  in  company  with  the  hepatic  artery  and  follow  its  ramifications  ; 
their  termination  is  unknown.  Ganglion-cells  occur  along  the  course  of 
the  nerves. 

The  secretion  of  the  liver,  the  bile,  frequently  contains  drops  of  fat, 
also  granular  masses  of  bile-pigment.  Columnar  cells  from  the  bile-ducts 
are  to  be  regarded  as  incidental  admixtures. 

That  the  structure  of  the  liver  really  follows  the  type  of  a  tubular 
gland  and  that  the  cords  of  hepatic  cells,  with  a  few  modifications,  are 
comparable  to  the  terminal  compartments  of  other  glands,  the  foregoing 


*  The  walls  of  the  veins  are  firmly  attached  to   the  liver  substance  by  the  interlobular 
connective  tissue  and  for  this  reason  they  do  not  collapse  when  cut. 


252 


HISTOLOGY. 


Excretory  duct. 


Artery. 


Capillaries. 


considerations  have   shown.     The  hepatic  lobules,  on  the  other  hand, 
cannot  without  explanation  be  compared  with  the  lobules  of  other  glands  ; 

the  latter  as  a  rule  consist  of  a  tubular 
system,  of  which  the  excretory  duct 
leaves  the  lobule  at  one  place  and  con- 
tinues into  a  larger  excretory  duct.  In 
the  hepatic  lobules  the  excretory  ducts 
emerge  at  many  points  on  the  surface  of 
the  lobule.  The  accompanying  schematic 
representations  may  serve  to  elucidate 
the  lobules.  Imagine  a  tubular  system  ; 
alongside  the  excretory  duct  runs  an 
artery,  the  capillaries  proceeding  from  it 
embrace  the  terminal  compartments  and 
open  into  a  vein  running  along  the  base 
of  the  terminal  pieces  (Fig.  187).  This 
is  the  principle  of  the  behavior  of  each 
of  the  many  tubular  systems  of  which 
the  liver  consists  ;  but  there  is  one  peculiarity  :  the  somewhat  tortuous 


Vein. 


Terminal 
compartments. 

FIG.  187.— SCHEME  OF  A  SYSTEM  OF  EX- 
CRETORY CHANNELS  ("  TUBULAR  SYS- 
TEM "). 


Excretory  ducts. 


Branch  of  portal  vein. 


Capillaries. 


Terminal  compartments. 


Central  veins. 


FIG.  188. — SCHEME  OF  THE  LIVER.  Two  lobules  are  shown,  of  which  the  left  is  only  half  carried  out. 
The  ramifications  and  anastomoses  of  the  capillaries  and  of  the  cords  of  hepatic  cells  have  been 
omitted  for  the  sake  of  clearness. 


THE    DIGESTIVE    ORGANS. 


253 


terminal  compartments  extend  in  different,  definite  directions  (Fig.  188). 
At  the  base  of  the  terminal  piece,  as  well  as  above,  runs  the  vein,  but — 
another  variation — the  vein  takes  up  not  only  these  capillaries  but  also 
those  of  another  side,*  for  there  lies  another  tubular  system,  the  terminal 
pieces  of  which  at  their  base  are  in  contact  with  the  same  vein.  The  vein, 
therefore,  lies  in  the  axis  of  a  complex  of  terminal  compartments  and  such 
a  complex  is  termed  an  hepatic  lobule.  If  now  we  draw  a  comparison  with 
the  scheme  Fig.  187,  the  artery  corresponds  to  the  portal  vein  in  scheme 


Branch  of  portal 
vein. 


Capillary. 


Central  vein. 


FIG.  189.— SCHEME  OF  A  TRANSVERSE  SECTION  OF  THE  LIVER.  Four  lobules  represented.  The  separate 
systems  of  ducts  are  indicated  by  the  difference  in  shading.  A.  Excretory  ducts.  E.  Terminal 
compartments. 

Fig.  1 88,  for  the  role  of  the  portal  vein  in  the  liver  is  the  same  as  that  of 
arterial  branches  in  other  glands,  and  the  vein  in  Fig.  187  is  the  equiv- 
alent of  the  central  vein  of  Fig.  188;  one  hepatic  lobule  corresponds, 
not  to  one  tubular  system,  but  to  parts  of  several  systems  (Fig.  189). 
For  the  sake  of  simplicity  this  schematic  presentation  is  based  on  the 
conception  of  well-defined  lobules,  as  they  occur  in  the  hog.  In  other 
animals  the  distribution  of  the  terminal  ramifications  is  less  regular ;  the 
latter  bend  into  neighboring  lobules,  to  which  in  part  is  owing  the  less 


*  In  the  liver  of  the  rabbit  the  central  veins  lie  close  under  the  surface  and  can  take  up 
the  capillaries  of  one  side  only. 


254 


HISTOLOGY. 


distinct  demarcation  of  the  lobules, 
the  formation  of  several  lobules. 


Each  tubular  system  participates  in 


THE  PERITONEUM. 

The  peritoneum  principally  consists  of  bundles  of  fibrous  connective 
tissue  and  numerous  elastic  networks  ;  the  free  surface  is  covered  by  a 
simple  layer  of  flat,  polygonal  epithelial-  (endothelial)  cells  ;  the  size  of 
these  cells  varies  according  to  the  stretching  to  which  they  are  subjected. 
The  connection  with  subjacent  parts  (the  parietes,  the  viscera,  etc.)  is 
effected  by  loose  (subserous)  connective  tissue  ;  in  the  peritoneum  re- 
flected over  the  small  intestine  the  endothelial  cells  send  delicate  processes 
into  the  subserous  tissue,  that  extend  into  the  muscularis. 

The  connective -tissue  bundles  are  arranged  in  thinner  (in  the  visceral 
peritoneum)  or  thicker  (in  the  parietal  peritoneum,  in  the  mesentery) 


,  x 


Epithelial-  (endo- 
thelial) cells. 


Nuclei  of  connective- 
tissue  cells. 


FIG.  190.— FROM  THE  GREATER  OMENTUMI-QF  A  RABBIT.  X  240.  The  network  is  formed  by  large  and 
small  bundles  of  connective  tissue.  The  wavy  striation  of  the  bundles  can  only  be  indistinctly  seen, 
because  the  preparation  is  mounted  in  damar. .  At  X  the  epithelial  cells  of  the  opposite  surface 
can  be  seen  shimmering  through.  Techn.  No.  120. 


layers,  chiefly  arranged  parallel  to  the  surface,  and  interlace  in  various 
directions  ;  in  certain  localities  (in  the  greater  omentum,  in  the  middle  of 
the  lesser  omentum)  the  bundles  form  a  beautiful  network  with  polygonal 
or  rectangular  meshes.  The  strands  of  the  network  also  are  covered  by 
flat  epithelial-cells  (Fig.  190). 

The  number  of  connective-tissue  cells  among  the  fibrous  bundles  is 
on  the  whole  not  large  ;  only  in  young  animals  are  larger  groups  of  cells 
found  ;  they  resemble  plasma-cells  and  all  probably  bear  a  close  relation 
to  the  formation  of  blood-vessels. 


THE    DIGESTIVE    ORGANS.  255 

The  clastic  fibers  in  the  deeper  layers  of  the  peritoneum,  particularly 
in  the  parietal  portion,  are  profuse  and  vigorously  developed. 

The  subscroiis  tissue  consists  of  loose  connective  tissue,  many  elastic 
fibers,  and  fat  varying  greatly  in  quantity  ;  it  is  plentiful  where  the  peri- 
toneum is  easily  shifted  over  the  underlying  parts,  but  on  the  liver  and 
the  intestine  so  much  reduced  that  it  cannot  be  demonstrated  as  a  special 
layer.  At  certain  places,  e.  g.y  in  the  broad  ligaments,  numerous  bands 
of  smooth  muscle-fibers  are  found. 

Blood-vessels  and  nerves  are  scantily  represented  ;  the  latter  partly 
terminate  in  lamellar  corpuscles. 

Lymph-vessels  occur  in  the  superficial  and  the  deeper  layers  of  the 
peritoneum. 

TECHN1C. 

No.  90. — Isolated  Squamoits  Cells  from  the  Oral  Cavity. — With  a 
scalpel  gently  scrape  the  upper  surface  of  the  tongue  and  mix  the  scrap- 
ings on  a  slide  with  a  drop  of  salt  solution  ;  apply  a  cover-glass  ;  in  ad- 
dition to  isolated,  pale,  squamous  epithelial-cells,  leucocytes  ("  salivary 
corpuscles")  may  be  found;  also,  with  more  vigorous  scraping,  the 
tips  of  filiform  papillae,  which  not  infrequently  are  surrounded  by  finely- 
granular,  dark  masses  of  micrococci  to  which  tufts  of  leptothrix  buccalis 
are  attached.  The  preparation  may  be  stained  under  the  cover-glass 
with  picrocarmine  and  then  treated  with  dilute  acidulated  glycerol,  pro- 
vided too  many  air-bubbles  do  not  make  the  preservation  of  the  prepara- 
tion impossible  (Fig.  7,  i). 

No.  91. — Mucous  Glands  of  the  Lips. — These  are  millet-sized  no- 
dules perceptible  to  touch  and  accessible  for  macroscopic  preparations. 
For  microscopic  preparations  cut  from  the  mucous  membrane  of  a  human 
lower  lip  (not  the  margin  of  the  lip)  I  cm.  cubes  ;  fix  them  in  50  c.c.  of 
Kleinenberg's  picrosulphuric  acid  and  in  twenty-four  hours  harden  in  50 
c.c.  of  gradually-strengthened  alcohol.  In  three  days  the  tissue  may  be 
sectioned.  Cut  many  sections,  not  too  thin,  and  stain  them  with  hema- 
toxylin  :  place  the  sections  in  water  and  with  the  naked  eye  select  those 
which  include  the  excretory  duct  and  preserve  them  in  damar ;  examine 
with  a  low  power  (Fig.  134). 

No.  92. — Dried  Ground  Tooth. — To  prepare  dried  ground  sections 
of  teeth  they  should  be  obtained  immediately  after  they  are  extracted, 
sawed  into  transverse  discs  2  mm.  thick,  glued  with  sealing-wax  upon 
cork  and  treated  like  No.  56.  If  longitudinal  sections  are  desired  the 
entire  tooth  should  be  glued  to  the  cork.  Longitudinal  sections  are  to 
be  preferred,  since  they  show  all  parts  of  the  tooth  in  a  single  preparation. 
If  it  is  desired  to  decalcify  the  teeth  of  an  adult,  proceed  as  with  No.  58. 
The  enamel  consisting  of  earthy  salts  and  only  from  3  to  5  per  cent,  of 
organic  substances  dissolves  completely,  so  that  only  the  dentine  and 
cementum  remain  (Fig.  135,  136,  137). 


256  HISTOLOGY. 

No.  93. — Odontoblasts. — Remove  the  teeth  from  the  jaws  of  a  new- 
born child  ;  place  them  in  60  c.c.  of  Muller's  fluid  ;  after  six  days  the 
pulp  can  be  easily  withdrawn  in  toto  by  means  of  forceps.  With  the 
scissors  cut  from  the  upper  surface  of  the  pulp  a  piece  the  size  of  a  len- 
til and  tease  a  little  the  tolerably  tenacious  tissue  in  a  drop  of  Muller's 
fluid  ;'  apply  a  cover-glass,  press  lightly  upon  it,  and  examine  with  the 
high  power.  At  the  edges  of  the  preparation  the  long  processes  of  the 
odontoblasts  standing  out  like  hairs  will  be  seen  ;  also  scattered,  com- 
pletely isolated  odontoblasts  (Fig.  139).  In  order  to  preserve,  treat 
under  the  cover-glass  with  distilled  water  for  two  minutes,  then  with  pic- 
rocarmine  ;  when  the  staining  is  completed,  add  dilute  acidulated  glycerol. 

No.  94. — Enamel  Prisms. — These  are  obtained  by  teasing  portions 
of  the  lateral  surface  of  the  teeth  of  No.  93  in  a  drop  of  Muller's  fluid. 
Examine  with  a  high  power.  The  enamel  prisms  will  be  found  in  groups 
of  three  and  more  ;  they  are  distinguished  by  their  dark  outlines  and 
usually  indistinct  cross-striation  (Fig.  138).  Mount  in  glycerol.  The 
prismatic  form  of  the  enamel  prisms  may  be  seen  in  thin  sections  cut 
parallel  to  the  surface  of  the  teeth.  Only  portions  of  a  section  exhibit 
regular  hexagonal  prisms,  that  is,  cross-sections  of  the  prisms  (Fig.  138). 
The  enamel  of  young  teeth  may  be  sectioned  without  previous  decalci- 
fication. 

No.  95. — Development  of  Teeth. — For  the  study  of  the  early  stages 
select  pig  and  sheep  embryos ;  these  are  the  most  easily  obtained  at  the 
slaughter  houses  ;  for  the  first  stage  the  pig  embryos  should  have  a  size 
of  about  6  cm.,  for  the  second  stage  a  size  of  about  10  or  1 1  cm.  For 
later  stages  the  inferior  maxilla  of  newborn  dogs  or  cats  is  very  suitable. 
Place  the  heads  (or  the  lower  jaws)  in  100  c.c.  of  Kleinenberg's  picrosul- 
phuric  acid  for  from  twelve  to  twenty -four  hours  and  harden  in  from  80  to 
1 20  c.c.  of  gradually-strengthened  alcohol.  After  the  heads  have  lain  six 
or  eight  days  in  90  per  cent,  alcohol,  they  are  to  be  decalcified  in  100 
c.c.  of  distilled  water  plus  I  or  2  c.c.  of  nitric  acid.  When  the  decalci- 
fication  is  completed,  in  from  three  to  eight  days,  harden  again  in 
alcohol.  In  five  or  six  days  cut  off  the  lower  jaw  and  divide  it  in  front 
in  the  middle  (larger  jaws  should  be  cut  vertically  into  pieces  I  or  2  cm. 
long)  ;  stain  the  pieces  in  bulk  in  borax-carmine.  When  the  staining 
and  decolorization  are  completed,  the  tissue  is  to  be  transferred  to  abso- 
lute alcohol,  in  which  it  must  remain  for  several  days  ;  it  is  then  to  be 
embedded  in  liver  and  sectioned.  It  is  necessary  to  cut  many  (20  to 
40)  thick  sections,  since  only  those  which  pass  through  the  middle  of 
the  tooth,  or  the  anlage  of  the  tooth,  can  be  used.  Mount  in  damar. 
Not  infrequently  in  sectioning  the  enamel  organ  is  lifted  from  the  papilla, 
so  that  a  free  space  exists  between  the  two.  The  dentine  is  often  stained 
in  different  tones  of  red  ;  this  is  due  to  the  different  ages  of  the  calcified 
and  uncalcified  strata  of  the  dentine.  The  objects  may  also  be  fixed  in 
Muller's  or  in  Zenker's  fluid  ;  section -staining  in  hematoxylin  is  not 
advisable,  since  too  many  sections  must  be  stained  which  on  investigation 
are  found  to  be  useless. 


THE    DIGESTIVE   ORGANS. 

\o  ^5. — PapilUe  Filifonncs,  Fnngiformes,  Circnm'callatce ;  Follicles 
of  the  Tongue. — Cut  pieces  2  cm.  square  from  the  mucous  membrane  of 
the  surface  of  a  human  tongue.  Each  piece  should  have  some  of  the 
muscle  tissue  attached  to  its  lower  surface  ;  for  fungiform  papillae  cut  the 
piece  from  the  tip  of  the  tongue  ;  for  filiform,  from  the  middle  of  the 
dorsum  of  the  tongue  ;  for  circumvallate,  from  the  root  of  the  tongue, 
and  for  follicles  (the  punctiform  openings  of  which  can  be  seen  with  the 
naked  eye)  from  the  root  of  the  tongue,  and  place  them  in  100  or  200 
c.c.  of  Mii Her' s  fluid.  The  fluid  must  be  changed  several  times  ;  after 
two  weeks  wash  the  tissue  and  harden  it  in  50  c.c.  of  gradually-strength- 
ened alcohol.  For  filiform  papillae  cut  thick  saggital  sections  of  the 
tongue  and  do  not  stain  them  ;  stain  the  other  sections  in  Hansen's 
hematoxylin  and  mount  in  damar  (Fig.  145,  146,  147).  For  the  prepa- 
rations represented  in  Fig.  148  and  Fig.  151  the  tissue  was  fixed  and 
hardened  in  50  c.c.  of  absolute  alcohol.  Rabbits'  tongues  may  be 
placed  in  toto  in  200  c.c.  of  Miiller's  fluid  ;  the  subsequent  treatment  is 
the  same.  Thick  cross-sections  through  the  anterior  half  of  the  entire 
tongue  are  suitable  for  the  study  of  the  arrangement  of  the  muscles  of 
the  tongue.  Thin  sections  of  the  root  of  the  tongue  show  beautiful 
mucous  and  serous  glands. 

No.  97. —  The  Tonsils. — The  tonsils  of  adult  man  do  not  furnish 
instructive  preparations.  They  should  be  treated  according  to  Techn. 
No.  96.  The  tonsils  of  the  rabbit  and  the  cat  are  recommended  ;  to 
find  them  proceed  as  follows. 

Dissect  the  skin  from  the  anterior  surface  of  the  neck  and  remove 
the  structures  lying  over  the  trachea  and  esophagus  ;  with  a  pair  of  stout 
scissors  cut  through  both  tubes  above  the  sternum,  grasp  the  cut  ends 
with  forceps  and  with  scissors  dissect  them  up  to  the  head  of  the 
pharynx,  keeping  close  to  the  anterior  surface  of  the  vertebral  column 
(at  the  same  time  the  cornua  of  the  hyoid  bone  will  be  divided).  Cut 
through  the  musculature  close  to  the  median  edges  of  the  inferior 
maxilla,  also  through  the  ligaments  of  the  tongue  (glosso-epiglottic). 
(In  the  rabbit  it  is  advisable  to  divide  both  angles  of  the  mouth,  and  with 
scissors  introduced  within  the  slit  to  sever  the  ligaments  and  the  genio- 
hyoglossus  muscle.)  Draw  the  trachea  and  attached  structures  down- 
ward, press  the  tongue  down  between  the  rami  of  the  inferior  maxilla, 
and  divide  its  remaining  attachments  (to  the  palate)  close  to  the  bone. 
Put  the  tongue  down  with  its  free  surface  looking  upward.  With  deli- 
cate scissors  divide  the  posterior  wall  of  the  pharynx  in  the  median  line 
down  to  the  larynx  and  pull  the  walls  apart ;  the  tonsils  will  then  be 
seen  as  a  pair  of  oval  prominences,  about  5  mm.  long,  on  the  lateral 
walls  of  the  pharynx.  They  may  be  fixed  in  60  c.c.  of  Kleinenberg's 
picrosulphuric  acid  (p.  21),  and  hardened  in  50  c.c.  of  gradually- 
strengthened  alcohols  (p.  33),  stained  with  hematoxylin  or  with  eosin 
and  hematoxylin  (p.  37),  and  mounted  in  damar. 

No.  98. — The  Esophagus. — Pieces  of  human  esophagus  2  cm.  square 
and  of  that  of  the  rabbit  and  cat  2  cm.  long  of  the  entire  tube  are  to  be 
17 


258  HISTOLOGY. 

fixed  in  60  c.c.  of  Miiller's  fluid  and  in  two  weeks  hardened  in  50  c.c. 
of  gradually-strengthened  alcohol  ;  stain  with  Hansen's  hematoxylin  ; 
mount  in  damar  (Fig.  152). 

No.  99. — The  Mucous  Membrane  of  the  Stomach. — For  topograph- 
ical preparations  place  pieces  from  2  to  5  cm.  square  for  six  hours  in  TOO 
c.c.  of  3  per  cent,  nitric  acid.  Remove  the  gastric  contents  adhering  to 
the  mucous  membrane  by  moving  it  slowly  to  and  fro  in  the  acid.  In  a 
half  hour  renew  the  acid  ;  harden  in  60  c.c.  of  gradually-strengthened 
alcohol.  Mount  thick  unstained  sections  in  damar  (Fig.  153). 

No.  100. — Fresh  Gastric  Glands. — From  the  fundus  of  the  stomach  of 
a  rabbit  just  killed  cut  pieces  about  2  cm.  square  and  separate  the  loosely- 
attached  muscular  coat  from  the  mucous  mem- 
brane. Grasp  the  latter  with  forceps  at  the  left 
edge  and  with  fine  scissors  cut  very  thin  strips,  0.5 
to  i  mm.  thick;  tease  them  in  a  drop  of  0.5  per 
cent,  salt  solution.  The  body  and  fundus  of  the 
fundus  glands  can  be  satisfactorily  isolated  without 
much  trouble.  The  protoplasm  of  theparietal-ce  11s 
can  be  distinctly  seen  (Fig.  191,  B),  the  chief-cells 
are  invisible.  The  nuclei  may  be  stained  with 
picrocarmine  and  the  preparation  mounted  in  dilute 
glycerol.  The  isolation  of  the  pylorus  glands  can 
only  be  accomplished  by  very  careful  teasing. 

No.  101. — Isolated  Gastric  Epithelium. — Place 
pieces    I  cm.  square  of  gastric  mucous  membrane 
FIG.  191.— LOWER  HALF  OF      for  about  five  hours  in  30  c.c.  of  Ranvier's  alcohol 

AN    ISOLATED     FUNDUS-        ,  r       1  \         T         i  • 

GLAND  OF  A  RABBIT,   x      (see  further  p.  2o).      In   the  majority  of  the   cells 

240.     B.  Parietal-cell ;  M,        \  Z  •  i  ,.    .    . 

membrana  propria.  the  mucous  portion  occupies  a  large  division  and 

they    have    the    appearance    of  those    pictured   in 

Fig.  I  5,  c.  The  preparation  may  be  stained  under  the  cover-glass  with 
picrocarmine,  and  mounted  in  diluted  acidulated  glycerol. 

No.  1 02. — Gastric  Glands. — The  stomach  of  a  cat  or  dog  that  if 
possible  has  been  fasting  for  one  or  two  days  is  especially  recommended. 
The  stomach  of  the  rabbit,  on  account  of  the  very  small  size  of  the  chief- 
cells,  is  less  suitable.  Dissect  off  the  mucous  membrane  from  the  mus- 
cular coat  and  place  pieces  of  the  former  about  I  cm.  square  in  about  10 
c.c.  of  absolute  alcohol.  In  about  a  half-hour  transfer  them  to  20  c.c.  of 
fresh  alcohol.  The  outlines  of  the  glands  can  be  recognized  in  moder- 
ately thin  sections  ;  the  only  difficulty  is  the  circumstance  that  the  gland- 
tubules  are  placed  very  close  together.  The  beginner  may  not  recognize 
the  glands  and  may  mistake  for  them  the  gastric  pits  lined  with  clear 
epithelium.  The  stomach  of  man,  which  however  is  suitable  for  use  only 
for  a  few  hours  after  death,  exhibits  this  difficulty  in  a  less  degree.  For 
the  study  of  the  minute  structure  of  the  glands  and  of  the  superficial 
epithelium,  embed  the  tissue  in  liver  and  cut  the  thinnest  possible 
sections. 


THE    DIGESTIVE    ORGANS.  259 

a.  For  fundus  glands i  chief-  and  parietal-cells,  cut  vertical  or,  better, 
horizontal  sections  of  the  mucous  membrane  and  stain  them  with  Hansen's 
hematoxylin  for  two   or  four  minutes.     Wash  the  sections  thoroughly 
ia  30  c.c.  of  distilled  water,  which  must  be  changed  as  often  as  it  becomes 
bluish — about  once  or  twice.     Transfer  them  to  5  c.c.  of  a  -^  per  cent, 
solution  of  Congo  red  (p.  25),  for  from  three  to  six  minutes,  wash  two' 
minutes  in  distilled  water  and  mount  in  damar.       If  the  sections  are  too 
thick,  everything  appears  red  ;  the  large  red  parietal-cells  cover  the  smaller 
chief-cells  ;    examine  the   thinnest  parts   of  the  sections,  especially  the 
fundi  of  the  glands,  where  the  parietal  cells  are  not  so  exceedingly  pro- 
fuse.    The  parietal  cells  can  be  recognized  with  the  low  power  as  isolated 
red  spots  on  a  rose-red  ground.    With  the  high  power  the  pale  blue  smaller 
chief-cells  can  be  seen.     The  very  narrow  lumen  of  the  fundus  glands 
may  be  best  seen  in  cross-sections  (sections  parallel  to  the  surface  of 
the  mucosa).     The  lateral  twigs  of  the  chief  lumen  can  only  be  perceived 
in  very  favorable    sections  (Fig.    155).      Fig.    154  is  a  combination  of 
several  thin  longitudinal  sections. 

b.  For  pylorus  glands,  stain  vertical  and  horizontal  sections  of  the 
mucosa  with  Hansen's  hematoxylin  and  mount  in  damar.     The  lumen  of 
the  pyloric  glands  is  wider  (Fig.  157).     Owing  to  the  extreme  sinuosity 
of  the  glands,  thin   sections  contain  but  few  glands  cut  in  their  entire 
length,  mostly  only  parts  of  them. 

No.  103. — Duodenal  Glands. — Cut  out  the  stomach  and  duodenum 
of  a  cat  about  one  hour  after  death.  Open  both  along  their  length, 
remove  the  contents  by  swaying  them  gently  to  and  fro  in  salt  solution 
(p.  19),  and  place  the  pyloric  end  of  the  stomach  and  the  upper  half  of 
the  duodenum,  in  all  a  piece  5  or  6  cm.  long,  for  six  hours  in  100  c.c.  of 
3  per  cent,  nitric  acid.  Further  treatment  like  No.  99.  Cut  longitudinal 
sections,  which  simultaneously  pass  through  pylorus  and  duodenum. 
Stain  with  Hansen's  hematoxylin.  Mount  in  glycerol  or  in  damar 
(Fig.  163).  If  the  tissue  be  placed  in  the  acid  immediately  after  death 
the  smooth  muscle  of  the  intestine  contracts  so  that  a  rigid  curving  of  the 
intestinal  wall  takes  place. 

No.    104. — Epithelium  and   Villi  of  tJie  Small  Intestine. — From  the 
middle  portion  of  the  small  intestine  of  a  rabbit  just 
killed,  cut  a  piece  one  cm.  long,   open   it  along   its  ^ 

length  and  remove  the  contents  by  carefully  pouring 
over  it  ^  per  cent,   salt  solution.     Then  grasp  the 
piece  at  the  left  edge  with  the  forceps,  with   fine  scis-         £" 
sors  cut  off  a  small  strip  and  spread  it  out  in  a  drop 
of  salt  solution  on  a  slide   on  a  black  background. 
With  the  unaided  eye  one  can  see  the  villi  projecting 
from  the  edge  of  the  preparation.      Examine  the  prep- 
aration    without    a    COVer-glaSS,  with    the    low    power.        FIG.  192.— INTESTINAL 
T^I  .n.        .n    ,  ",  ,     ,  ,,  VILLUS  OF  A  RABBIT. 

I  he  villi  will   be  seen  partly  extended,  partly  con-        x  70. 

tracted ;  the  latter  condition   may  be  recognized   by 

transverse  folds  running  across  the  villi  (Fig.  192).     Details  cannot  be 


26O  HISTOLOGY. 

detected.  Apply  a  cover-glass ;  the  villi  thus  become  flattened  and 
appear  clearer ;  the  cylindrical  epithelium  and  close  beneath  this  the 
loops  of  the  capillary  blood-vessels  can  be  distinctly  seen.  If  the  epithe- 
lium contains  goblet-cells,  these  appear  as  bright  shining  rounded  spots. 
For  the  investigation  of  the  epithelium,  proceed  as  follows  : — 

a.  Tease  the  piece  a  little  ;  in  this  way  columnar  cells,  singly  and  in 
groups,  may  be  isolated,  which  are  to  be  examined  with  the  high  power. 
Not  infrequently  some  columnar  cells  are  found  inflated  and  of  a  spherical 
form.       The  basal  border  sometimes  shows  very  distinct  rods.       Goblet- 
cells,  when  present,  may  be  recognized  by  their  homogeneous  appearance 
and  if  carefully  focused  the  sharply-outlined  orifice  may  be  perceived. 
Occasionally  the  epithelial-cells  are  difficult  to  loosen  from  the  basement- 
membrane  ;  in  such  cases  make  a  second  investigation  an  hour  later, 
when  the  epithelium  will  be  sufficiently  macerated  to  be  brushed  off. 

b.  For  permanent  preparations  place   pieces  (i  cm.  square)  of  the 
intestine  in  30  c.c.  of  Miiller's  fluid.    In  three  or  five  days  take  the  tissue 
out,  scrape   it  with   the   tip  of  a   scalpel,  and  distribute  a  little  of  the 
scraping  in  a  drop  of  diluted   glycerol  ;  cover-glass  ;  high   power  (Fig. 
161,  A). 

No.  105. — Sections  of  the  Small  Intestine. — Place  pieces  from  2  to 
4  cm.  long  of  the  intestine  of  a  rabbit,  better,  of  a  puppy  or  a  kitten,. in 
100  or  200  c.c.  of  3  per  cent,  nitric  acid.  After"  six  hours  the  pieces 
are  to  be  hardened  in  100  c.c.  of  gradually-strengthened  alcohol.  Sec- 
tions can  be  made  through  the  entire  intestinal  tube ;  in  most  cases,  only 
fragments  of  the  villi  are  thus  obtained  ;  to  obtain  entire  villi,  with  a  razor 
cut  open  the  hardened  intestine  along  its  length,  pin  it  with  needles  on  a 
cork-plate,  with  the  mucosa  uppermost.  The  villi  can  then  be  seen  with 
the  unaided  eye.  Cut  thick  cross-sections,  stain  them  for  one  minute 
with  Hansen's  hematoxylin  and  mount  in  damar.  Goblet-cells  are 
very  frequently  found  in  the -epithelium  (Fig.  161,  B).  Staining  in  bulk 
with  borax-carmine  is  highly  recommended. 

The  human  intestine,  before  being  placed  in  the  nitric  acid,  must 
be  cut  open  and  washed  in  the  same  fluid.  It  is  advisable  to  pin  pieces 
about  5  cm.  square  to  a  cork-plate  and  thus  to  place  them  in  the  fixing 
and  hardening  fluids.  If  the  intestine  is  not  absolutely  fresh,  the  entire 
superficial  epithelium  loosens  so  that  the  naked  connective-tissue  villi  lie 
exposed. 

Horizontal  sections  of  the  intestine  furnish  very  beautiful  pictures. 
Not  infrequently  the  cross-sections  of  the  glands  drop  out  and  then  only 
the  connective-tissue  tunica  propria  remains.  In  these  preparations  the 
goblet-cells  all  appear  as  clear  bodies  of  equal  size  and  therefore  afford 
no  clue  in  regard  to  the  functional  state  of  the  cell. 

For  the  latter  purpose  the  following  is  recommended  : — 

No.  1 06. — Triple  Staining  of  the  Intestine. — Small  pieces  of  tissue 
are  to  be  fixed  in  Flemming's  mixture  (p.  22),  hardened  in  gradually- 
strengthened  alcohol,  and  subsequently  treated  according  to  the  method 
given  on  page  40,  10. 


THE    DIGESTIVE    ORGANS.  26 1 

No.  107. — Agin ina fed  Xodules  (Pate  lies  of  Peyer). — These  can  be 
seen  shimmering  through  the  uninjured  fresh  intestinal  wall  of  the  rab- 
bit, but  in  the  dog  and  in  the  cat  (on  account  of  the  thickness  of  the  mus- 
cuhir  coat)  often  they  are  not  perceptible.  In  the  latter  animals  patches 
are  constant  at  the  point  where  the  small  intestine  opens  into  the  large. 
Cut  out  the  portion  of  the  intestine  of  a  rabbit  containing  the  Peyer's 
patches  and  proceed  according  to  the  method  given  in  No.  105.  In  the 
cat  take  the  lowermost  portion  of  the  ileum  (about  2  cm.  long)  with  a 
piece  of  the  cecum  of  the  same  length  ;  open  both  along  their  length  and 
span  them  out  on  a  cork-plate,  with  the  mucosa  uppermost.  Usually 
the  mucosa  is  covered  with  a  tenaceous  excrement,  difficult  to  remove  by 
washing,  which  glues  the  villi  together,  so  that  only  oblique  sections  of 
the  villi  can  be  obtained.  Further  treatment  like  No.  105. 

Closely-placed  nodules  are  found  in  the  blind  half  of  the  vermiform 
process  of  the  rabbit,  which  encroach  upon  the  mucosa  and  compress  it 
to  such  narrow  areas  that  cross-sections  exhibit  very  complicated  pic- 
tures, scarcely  intelligible  to  the  beginner. 

Fixation  in  o.  I  per  cent,  chromic  acid  and  hardening  in  gradually- 
strengthened  alcohols  renders  the  germinal  centers  very  distinct,  but  is 
not  so  good  for  the  remaining"  elements  as  the  nitric  acid. 

o  o 

No.  1 08. — The  Large  Intestine. — Treat  empty  pieces  like  No.  105 
or  No.  1 06  (compare  with  Fig.  16,  p.  70).  Pieces  filled  with  feces  must 
be  cut  open,  washed,  and  spanned  on  cork. 

.  No.  109. — Fresh  Crypts  of  the  Large  Intestine  of  the  Rabbit. — Cut  a 
piece  i  cm.  long  from  the  lowermost  portion  of  the  large  intestine  (be- 
tween two  spherical  masses  of  feces),  place  it  on  a  dry 
slide,  open  it  with  the  scissors  and  spread  it  out  with 
the  mucous  surface  uppermost ;  add  a  drop  of  ^  per 
cent,  salt  solution,  grasp  the  piece  with  forceps  at  the 
left  edge  and  with  fine  scissors  cut  off  an  extremely 
thin  strip.     Transfer  this  with  a  drop  of  the  salt  solu- 
tion to  another  slide ;   with  needles  separate  the  mus- 
cularis  from  the  mucosa  and  tease  the  latter  a  very 
little  ;  apply  a  cover-glass  with  slight  pressure.     With 
a  low  power  the  crypts  can  be  readily  seen,  but  it  is 
difficult  to  detect  their  orifices  (Fig.  193).     The  epi-      FIG    ^  _^   Epkhe_ 
thelial-cells  are  often  granular  in  the  portion  border-        Hum ;  A  crypts,  xso. 
ing  the  lumen.     With  the  high  power  the  superficial 
epithelium   can  be  very  well  seen  from  the  side  and  from  the  surface. 
The   contents  of  the   goblet-cells  often  are  not  clear,  as  in  sections,  but 
dark  and  granular. 

No.  110. — Blood-vessels  of  the  Stomach  and  the  Intestines. — A 
stomach  and  intestine  injected  from  the  descending  aorta  are  to  be  fixed  in 
from  50  to  200  c.c.  of  Miiller's  fluid  and  hardened  in  gradually-strength- 
ened alcohols.  One  portion  should  be  cut  into  thick  (up  to  I  mm.)  sec- 
tions, stained,  and  mounted  in  damar  (Fig.  166),  and  another  part  used 


262  HISTOLOGY. 

for  horizontal  preparations,  which  with  the  low  power  and  change  of 
focus  are  very  instructive.  For  this  purpose  pieces  of  the  large  intestine 
i  cm.  square  may  be  transferred  from  absolute  alcohol  to  5  c.c.  of 
turpentine  for  clearing  and  mounted  in  damar.  It  is  also  easy  to  strip 
the  muscularis  from  the  mucosa  and  to  mount  the  separate  coats  in 
damar. 

No.  1 1 1. — Auerbach  s  and  Meissner 's  Plexus. — For  this  purpose  in- 
testines with  a  thin  muscular  coat  are  preferable,  therefore  the  intestine 
of  the  rabbit  and  guinea-pig  (not  of  the  cat)  are  especially  suitable.  It  is 
not  necessary  that  the  object  be  absolutely  fresh  ;  the  small  intestines  of 
children  several  days  after  death  can  still  be  used.  Prepare  200  c.c.  of 
a  dilute  solution  of  acetic  acid  (10  drops  of  glacial  acetic  acid  to  200  c.c. 
of  distilled  water).  Then  separate  a  piece  (from  10  to  30  cm.  long)  of 
the  small  intestine  from  the  mesentery.  Cut  it  off  and  with  the  finger 
lightly  press  out  the  contents  ;  tie  the  lower  end  of  the  intestine  and  fill 
it  from  the  upper  end  with  the  dilute  acetic  acid  ;  tie  it  above  and 
place  the  whole  piece  in  the' remainder  of  the  acetic  acid.  In  one  hour 
change  the  fluid.  In  twenty-four  hours  transfer  the  intestine  to  dis- 
tilled water,  with  scissors  open  it  along  one  side  of  the  line  of  attach- 
ment of  the  mesentery  and  cut  off  a  piece  I  cm.  long.  The  muscularis 
can  be  readily  separated  from  the  mucosa  with  the  aid  of  forceps  ; 
they  are  only  firmly  united  at  attachment  of  the  mesentery. 

a.  Plexus  Myentericus. — If  a  piece  of  black  paper  be  placed  under 
the  glass  dish  containing  the  tissue,  the  white  nodal  points  of  Auerbach's 
plexus  can  be  seen  by  the  unaided  eye.     Transfer  a  piece  of  the  muscu- 
laris, about  i  cm.  square,  in  a  drop  of  the  dilute  acetic  acid  to  a  slide  ;  ex- 
amined with  the  lower  power  it  furnishes  a  very  pretty  picture  (Fig.  167, 
A).      If  it  is  desired  to  preserve  thepreparation,  place  the  tissue  for  one 
hour  in  30  c.c.  of  distilled  water,  which  must  be  changed  several  times, 
and  then  for  from  eight  to  sixteen  hours  in  5  or  10  c.c.  of  a  I   per  cent, 
osmic  acid  solution,  in  the  dark  ;  wash  the  piece  quickly  in  distilled  water 
and  mount  in  diluted  glycerol.     The  osmium  preparations  are   not  as 
beautiful  as  the  fresh  ones  in  the  acetic  acid.      In   the  guinea-pig  both 
strata  of  the  muscularis  can  be  readily  separated  (if  the  intestine  is  abso- 
lutely fresh  on  being  filled  with  the  dilute  acid)  ;  the  plexus  remains  at- 
tached to  one  stratum.      Pieces  of  this  should  be  placed  for  one  hour  in 
distilled  water,  then  treated  with  gold  chlorid  (p.   43),  and  mounted  in 
damar.     The  gold-chlorid  treatment  is  less  adapted  to  human  intestines, 
since  both  the  muscular  layers  are  likewise  stained  red  and  partially  con- 
ceal  the  plexus.     The  firm  union  of  the  muscular  strata  in  the  human 
organ  may  be  due  to  the  age  of  the  object. 

b.  Plexus  Submucosus. — With  a  scalpel  scrape  the  epithelium  from 
the  isolated  mucosa  ;  place  a  piece  about  I  cm.  square  on  a  slide  ;  apply 
a  cover-glass,  press  upon  it  slightly,  and  examine  with  the  low  power  (Fig. 
167,  B).     To  preserve  the  preparation,  proceed  as  in  No.  1 1 1,  a  ;  but  it 
is    advisable   to  span  the  pieces   on  cork  and  before  transferring  them 
from  the  ninety-five  per  cent,  alcohol  to  the  bergamot  oil,  to  press  them 


THE    DIGESTIVE    ORGANS.  263 

somewhat,  in  order  that  the  alcohol  may  be  completely  removed  from  the 
spongy  mucosa. 

In  addition  to  nerves  many  blood-vessels  are  present,  which  may 
be  easily  recognized  by  the  structure  of  their  walls,  in  part  by  the  trans- 
versely-placed nuclei  of  the  muscle-fibers. 

No.  112. — The  Parotid^  Submaxillary ,  and  Sublingual  Glands. — 
From  human  glands  (in  winter  useful  after  three  or  four  days)  cut  a  num- 
ber of  pieces  from  0.5  to  I  cm.  square  and  place  them  in  30  c.c.  of  Zen- 
ker's  fluid  (for  further  treatment,  see  p.  31).  Stain  one  piece  in  bulk  in 
borax-carmine.  Embed  another  in  liver  and  cut  the  thinnest  possible 
sections  ;  small  fragments  about  2  mm.  long  can  be  used  ;  stain  them  in 
Hansen's  hematoxylin,  two  or  three  minutes  ;  the  transfer  of  the  sections  to 
the  staining  solution  must  be  done  slowly,  or  the  most  delicate  sections  will 
be  destroyed  ;  then  stain  with  eosin  (p.  37),  and  mount  in  damar.  (Very 
thin  sections  should  be  examined  in  water  after  the  staining  in  hema- 
toxylin is  completed,  since  the  cell  boundaries  are  then  very  much  more 
distinct).  If  the  staining  is  successful,  the  salivary  tubules  and  the  cres- 
cents are  red.  In  the  sublingual  gland  and  in  the  mucous  cells  of  the 
submaxillary  the  membrana  propria  also  stains  red  ;  it  must  not  be  con- 
fused with  the  sections  of  the  crescents,  which  latter  are  granular,  while 
the  membrana  propria  has  a  homogeneous  appearance.  The  mucous  cells 
in  the  borax-carmine  preparations  are  clear  throughout.  In  the  sections 
stained  with  hematoxylin  they  are  sometimes  clear,  sometimes  a  pale 
blue  of  different  shades  (Fig.  168)  ;  the  portion  which  stains  is  a  re- 
ticulum  which  occurs  in  certain  functional  stages  of  each  mucous  cell. 
The  very  short  intercalated  pieces  of  the  submaxillary  gland  are  difficult 
to  find  ;  on  the  other  hand,  they  may  be  easily  seen  in  the  parotid  (Fig. 
169,  s)  (also  in  that  of  the  rabbit).  Of  the  end-pieces  only  certain  por- 
tions, those  which  have  been  accurately  halved  and  the  lumen  of  which 
is  visible,  are  suitable  for  study.  The  numerous  oblique  and  tangential 
sections  are  often  very  difficult  to  understand  (Fig.  168,  4,  5,  6,  7). 

No.  1 13. — The  Pancreas. — The  human  pancreas  as  a  rule  cannot  be 
used.  The  treatment  is  the  same  as  for  the  parotid  gland,  No.  112. 
The  characteristic  granular  zone  of  the  gland-cells  bordering  the  lumen 
is  not  to  be  seen  by  this  method  (Fig.  171,  B).  Tease  a  pinhead-sized 
piece  of  the  fresh  pancreas  of  a  cat  in  a  drop  of  ^  per  cent,  salt  solu- 
tion. With  the  low  power  the  end-pieces  appear  spotted ;  this  is  due  to 
the  partly  clear  and  partly  granular  divisions  of  the  cell.  With  high 
magnification  the  tissue  appears  like. Fig.  171,  A. 

No.  114. — Liver  Cells. — Make  an  incision  in  a  fresh  liver  and  with 
the  blade  of  a  scalpel  obliquely  placed  scrape  the  cut  surface.  The 
brown  liver-tissue  adhering  to  the. blade  is  to  be  transferred  to  a  slide 
and  a  drop  of  salt  solution  added.  Apply  a  cover-glass.  Examine  first 
with  the  low  power  then  with  the  high  (Fig.  176,  A).  In  addition  to  the 
liver-cells,  the  preparation  contains  numerous  colored  and  colorless 
blood-corpuscles. 


264  HISTOLOGY. 

No.  1 15. — Hepatic  Lobules. — Place  small  pieces  (about  2  cm.  cubes) 
of  a  pig's  liver  in  from  30  to  50  c.c.  of  absolute  alcohol.  The  majority 
of  the  lobules  are  hexagonal ;  they  can  be  seen  on  the  surface  of  the 
liver  by  the  unaided  eye  and  after  a  moment  become  distinctly  visible  on 
the  cut  surface.  The  section  of  the  central  vein  also  becomes  visible.  In 
about  three  days  sections  can  be  made  ;  stain  them  with  Hansen's  hema- 
toxylin.  The  division  into  lobules  can  be  well  seen  with  the  low  power, 
but  the  hepatic  cells  as  well  as  the  bile-ducts  are  less  satisfactory  for 
study.  Better  for  this  purpose  is  the  following. 

No.  1 1 6. — Human  Liver. — Place  pieces  about  2  cm.  square,  as  fresh 
as  possible,  for  four  weeks  in  200  c.c.  of  Miiller's  fluid  for  fixation  and 
then  in  100  c.c.  of  gradually-strengthened  alcohols  for  hardening.  Ex- 
amine unstained  sections  (cut  parallel  and  also  vertical  to  the  surface)  and 
stain  others  with  Hansen's  hematoxylin  and  eosin  ;  mount  in  damar. 
The  demarcation  of  the  lobules  is  not  distinct,  because  of  the  slight 
development  of  the  interlobular  connective  tissue.  The  division  into 
lobules  may  be  more  readily  perceived  on  macroscopic  inspection,  than 
on  investigation  with  the  microscope.  For  orientation  the  beginner 
should  recall  that  isolated  sections  of  blood-vessels  always  represent  in- 
tralobular  veins  ;  while  groups  of  such  sections  represent  branches  of  the 
portal  vein,  of  the  hepatic  artery,  and  of  the  bile-duct.  Exact  trans- 
verse sections  of  central  veins  may  also  be  recognized  by  the  cords  of 
hepatic  cells  radiating  from  them  (Fig.  177).  For  the  study  of  the 
structure  of  the  gall-bladder  as  well  as  of  the  larger  bile-ducts,  only 
absolutely  fresh  livers  can  be  used,  since  the  alkaline  bile  permeates  the 
walls  of  the  gall-bladder  soon  after  death,  stains  the  tissue  yellow,  and 
renders  it  unfit  for  microscopic  investigation. 

No.  117. — To  demonstrate  the  capillaries  and  the  intralobular  con- 
nective tissue,  which  in  ordinary  preparations  are  scarcely  visible,  shake 
a  number  of  thin  double-stained  sections  of  human  liver  (No.  116)  for 
from  two  to  three  minutes  in  a  test-tube  half  filled  with  distilled  water. 
The  liver-cells  in  part  fall  out ;  the  edges  of  the  preparation  are  then  to 
be  examined  in  a  drop  of  water  (Fig.  186).  This  preparation  can  be 
mounted  in  damar,  but  the  more  delicate  connective-tissue  fibers  disap- 
pear therein. 

No.  1 1 8. — Blood-  Vessels  of  the  Liver. 

'  a.  Chloroform  a  rabbit  and  quickly  place  a  2  cm.  cube  of  liver 
(without  allowing  much  blood  to  flow  from  it)  in  50  c.c.  of  absolute  al- 
cohol. In  two  days  the  natural  injection  can  be  seen  on  the  surface  ;  it 
is  indicated  by  brown  spots  within  the  centers  of  the  lobules.  Cut  thick 
sections  parallel  to  the  surface  and  mount  them  unstained  in  damar. 
Examine  with  a  low  power.  Very  frequently  only  the  superficial  strata 
of  the  liver  contain  filled  blood-vessels: 

b.  Of  all  injections  that  of  the  liver  is  most  easily  accomplished. 
Inject  Berlin  blue  (p.  43),  either  through  the  portal  vein  or  the  inferior 
vena  cava  ;  in  the  latter  case  it  is  advisable  to  make  an  incision  above 


THE    DIGESTIVE    ORGANS.  265 

the  diaphragm,  to  allow  the  heart  to  rest  upon  the  latter,  and  to  insert 
the  canula  through  the  right  auricle  into  the  inferior  cava.  The  injected 
liver  is  to  be  placed  in  toto  in  about  500  c.c.  of  Muller's  fluid ;  after  six 
days  pieces  about  2  cm.  square  of  the  portions  best  injected  are  to  be  cut 
out,  again  placed  for  two  or  three  weeks  in  about  1 50  c.c.  of  Muller's 
fluid,  and  "finally  hardened  in  100  c.c.  of  gradually-strengthened  alcohols. 
Cut  thick  sections  and  mount  them  unstained  in  damar  (Fig.  180,  181, 
182). 

No.  1 19. — Exhibition  of  Gland  Lnmina  by  Golgi'  s  "  Black  Reaction." 
— Place  small  pieces  of  the  root  of  the  tongue,  of  the  stomach,  of  the 
salivary  glands,  and  of  the  liver  for  three  days  in  the  osmio-bichromate 
mixture  (in  winter,  in  the  warm  chamber),  and  for  the  same  length  of 
time  in  the  silver  solution.  For  further  treatment  see  page  41.  Very 
often  the  staining  does  not  succeed  until  after  the  procedure  has  been 
repeated  one  or  twice.  After-staining  (p.  42)  is  advised.  In  the  liver 
the  "lattice-fibers  "  occasionally  stain. 

No.  1 20. — The  Endothelium  of  the  Peritoneum. — Proceed  as  in  No. 
38,  but  instead  of  taking  the  mesentery,  which  also  yields  instructive 
pictures,  use  the  greater  omentum.  The  pieces  may  be  stained  in  Han- 
sen's  hematoxylin  and  mounted  in  damar  (Fig.  190). 


VII.  THE  RESPIRATORY  ORGANS. 

THE  LARYNX. 

The  mucous  membrane  of  the  larynx  is  a  continuation  of  the  pharyn- 
geal  mucous  membrane  and  like  this  is  composed  of  an  epithelium,  a 
tunica  propria,  and  a  submucosa,  which  latter  connects  the  mucous 
membrane  with  underlying  parts.  The  mucous  membrane  over  nearly 
the  whole  of  the  organ  is  covered  by  a  stratified  ciliated  columnar  epi- 
thelium;  the  ciliary  wave  is  directed  toward  the  cavity  of  the  pharynx. 
On  the  true  vocal  cords,  on  the  anterior  surface  of  the  arytenoid  cartilages 
and  on  the  laryngeal  surface  of  the  epiglottis  the  epithelium  is  of  the 
stratified  scaly  variety.  The  tunica  propria  consists  of  numerous  elastic 
fibers  and  of  fibrous  connective  tissue,  which  in  the  lower  animals  is  con- 
densed to  a  membrana  propria  immediately  beneath  the  epithelium. 
The  tunica  propria  is  the  site  of  a  varying  number  of  leucocytes  ;  in  dogs 
and  cats,  solitary  nodules  (p.  125)  are  found  in  the  mucous  membrane 
of  the  ventricle  of  the  larynx  (Morgagni).  Papillae  mainly  occur  in  the 
mucous  membrane  clothed  with  stratified  squamous  epithelium  ;  on  the 
free  border  and  on  the  lower  surface  of  the  vocal  cords  the  papillae  are 
merged  in  longitudinal  ridges.  The  submucosa  contains  branched  tubu- 
lar mucous  glands  from  0.2  to  I  mm.  in  size. 

The  cartilages  of  the  larynx  principally  consist  of  the  hyaline 
variety,  which  in  a  measure  exhibits  the  peculiarities  of  the  costal  cartil- 
age. The  hyaline  cartilages  are  the  thyroid,  the  cricoid,  the  greater 
portion  of  the  arytenoids,  and  often  the  triticeous  cartilages.  The  epiglot- 
tis, the  cuneiform  cartilages  (Wrisberg),  the  cornicular  cartilages  (San- 
torini),  the  median  portion  of  the  thyroid,  and  the  apex  and  vocal  process 
of  the  arytenoid  cartilages  are  of  the  yellow  elastic  variety.  Occasion- 
ally the  triticeous  cartilages  are  composed  of  fibro-cartilage.  Between 
the  twentieth  and  thirtieth  years  of  life  ossification  (chiefly  endochondral) 
begins  in  the  thyroid  and  the  cricoid  cartilages. 

The  larynx  is  richly  supplied  with  blood-vessels  and  .nerves.  The 
blood-vessels  form  two  or  three  networks  extending  in  planes  parallel 
to  the  surface  and  a  close  subepithelial  capillary  plexus. 

The  lymph-vessels  form  two  communicating  networks  also  extending 

266 


THE    RESPIRATORY    ORGANS.  26/ 

in  horizontal  planes,  of  which  the  superficial  consists  of  narrower  chan- 
nels and  lies  beneath  the  vascular  capillary  network. 

The  nerves  in   their  course  include  microscopic  ganglia.      In  part 
they  terminate  in  end-bulbs  and  in  taste-buds. 


THE  TRACHEA. 

The  ciliated  mucous  membrane  of  the  trachea  possesses  a  structure 
like  that  in  the  larynx,  excepting  only  that  the  elastic  fibers  form  a  close 
network  in  which  the  fibers  pursuing  a  longitudinal  direction  predomi- 
nate. This  network  lies  immediately  beneath  the  epithelium,  above  the 
glands.  The  cartilages  are  of  the  hyaline  variety.  The  posterior  wall 
of  the  trachea  is  composed  of  a  layer  of  transversely-arranged  smooth 
muscle-fibers,  that  usually^  is  covered  by  a  stratum  of  muscle-fibers 
extending  longitudinally.  The  mucous  glands  of  the  posterior  wall  are 
distinguished  by  their  size  (2  mm.)  ;  they  not  infrequently  penetrate  the 
muscular  layer,  so  that  they  lie  in  part  in  the  fibrous  tissue  behind  it. 

The  behavior  of  the  blood-vessels,  lymph-vessels,  and  nerves  is  the 
same  as  in  the  larynx. 

THE  BRONCHI  AND  THE  LUNGS. 

The  lungs  may  be  regarded  as  compound  alveolar  glands,  in  which, 
as  in  all  glands,  excretory  and  secretory  (in  this  case  respiratory)  por- 
tions maybe  distinguished.  The  excretory  division  comprises  the  larynx, 
the  trachea,  and  the  bronchi.  |  Each  bronchus  on  entering  the  lung 
divides  repeatedly  and  within  the  same  undergoes  continual  subdivision, 
by  direct  giving  off  small  lateral  twigs,  by  branching  at  acute  angles, 
and  by  gradual  decrease  in  the  caliber  of  the  large  branches  ;  in  this 
way  each  bronchus  breaks  up  into  minute  twigs,  that  nowhere  anasto- 
mose with  one  another  and  that  retain  the  characteristics  of  the  excre- 
tory duct  to  a  diameter  of  0.5  mm. 

At  this  point  the  respiratory  division  begins.  Small,  isolated,  hemi- 
spherical evaginations,  the  alveoli,  appear  at  irregular  intervals  on  the 
walls  of  the  minute  bronchi.  Such  bronchi  are  called  respiratory  or 
terminal  bronchioles.  These  divide  and  lead  into  the  alveolar  ducts,  which 
differ  from  the  bronchioles  only  in  the  larger  number  of  alveoli  in  their 
walls.  The  alveolar  ducts  divide  at  right  or  acute  angles  and  pass  with- 
out sharp  demarcation  into  the  slightly-expanded  blind  terminal  vesicles 
(less  correctly,  infundibula),  the  walls  of  which  are  thickly  beset  with 
alveoli.  Each  alveolus  is  open,  not  only  toward  the  terminal  vesicle, — 


268 


HISTOLOGY. 


this  broad  opening  is  termed  base — but  also  is  in  direct  communication 
with  neighboring  alveoli  by  means  of  minute  canals,  the  so-called  pores. 

The  entire  respiratory  division  is  separated  by  areolar  tissue  into 
lobules  from  0.3  to  3  cm.  in  size.  All  the  branches  of  the  excretory 
division  to.  a  diameter  of  from  1.5  to  I  mm.  and  less  lie  between  the 
lobules,  as  "  interlobular  ducts." 

The  minute  structure  of -the  bronchi  in  the  largest  branches  does  not 


Tunica 
Epithelium.  propria. 


\lveoli. 


Excretory  duct 
of  gland. 


FIG.  194.— CROSS-SECTION  OF  A  BRONCHUS,  Two  MILLIMETERS  THICK,  OF  A  CHILD.    X  30. 

Techn.  No.  123. 

differ  from  that  of  the  trachea.  Gradually  modifications  appear,  which  first 
involve  the  cartilages  and  the  musculature.  The  C-shaped  ring  cartilages 
are  replaced  by  irregular  plates  lying  on  all  sides  of  the  bronchial  wall. 
They  diminish  in  size  and  thickness  with  the  decrease  in  the  diameter  of 
the  bronchi  and  disappear  in  bronchioles  I  mm.  in  diameter. 

The   smooth  muscle-fibers  are  circularly  disposed  in  a   continuous 
layer  lying  within  the  cartilages  and  form  a  complete  investment  for  the 


THE    RESPIRATORY    ORGANS.  269 

tube.  The  thickness  of  the  muscular  layer  decreases  with  the  diameter 
of  the  bronchi ;  but  muscle-fibers  are  still  found  as  far  as  the  alveolar 
ducts.  They  are  wanting  in  the  terminal  vesicle's. 

The  mucous  membrane  is  thrown  into  longitudinal  folds  and  con- 
sists of  a  stratified  ciliated  epithelium  containing  goblet-cells,  that  in  the 
smaller  bronchi  becomes  gradually  reduced  to  a  single  stratum,  and  of 
a  connective-tissue  tunica  propria.  The  latter  contains  numerous  longiT 
tudinal  networks  of  elastic  fibers  and  leucocytes  in  greatly  varying  num- 
bers. Occasionally  the  latter  form  solitary  nodules,  from  the  crest  of 
which  leucocytes  wander  through  the  epithelium  into  the  bronchial  tube. 

Branched  tubular  mucous  glands  occur  as  far  as  the  cartilages  ex- 
tend ;  they  are  situated  outside  of  the  muscula-r  layer  (Fig.  194).  They 
are  numerous  and  do  not  disappear  until  at  the  beginning  of  the  respira- 
tory bronchioles. 

External  to  the  cartilages  is  a  fibro-elastic  tunic,  which  envelops  the 
entire  bronchus  including  the  accompanying  vessels  and  nerves. 

The  minute  structure  of  the  respiratory  division,  after  the  gradual  dis- 
appearance of  cartilages  and  glands,  is  distinguished  in  particular  by  the 
nature  of  the  epithelium. 

The  respiratory  bronchioles  following  the  smallest  excretory  bronchi 


Terminal  Bronchiole.     \  , 
Alveoli.  ^£ 


Alveoli. 


Alveolar  duct. 


FIG.  195.— FROM  A  SECTION  OF  LUNG  OF  ADULT  MAN.  X  50.  The  terminal  bronchiole  divides  into  two 
branches  (on  the  right).  A  portion  of  the  wall  of  the  bronchiole  fell  within  the  plane  of  the  section  ; 
here  the  entrance  to  the  alveoli  is  seen  from  above;  in  the  lower  branch  the  alveoli  are  viewed  from 
the  side.  The  epithelium  of  the  bronchiole  is  mixed.  The  epithelial  lining  of  the  alveoli  is  only  par- 
tially visible  with  this  magnification.  Techn.  No.  124. 

at  the  beginning  still  contain  a  single  layer  of  ciliated  columnar  epithe- 
lium ;  as  they  proceed  the  cilia  are  lost,  the  cells  become  cubical,  and 
between  these  another  kind  of  epithelial- eel  Is  appears,  in  the  form  of 
thin  nonnucleated  plates  of  different  sizes.  These  plates  and  isolated 
or  small  groups  of  cubical  cells  form  an  epithelium  called  respiratory 


2/0 


HISTOLOGY. 


epithelium.  The  transition  of  the  cubical  epithelium  into  the  respiratory 
epithelium  is  not  abrupt,  but  occurs  in  such  wise  that  at  one  extremity 
of  the  bronchiole  cubical,  at  the  other  extremity  respiratory  epithelium 
is  found,  or  that  groups  of  cubical  cells  are  surrounded  by  respiratory 
epithelium  and  the  reverse.  Hence  the  respiratory  bronchioles  contain 
a  mixed  epithelium  (Fig.  195  and  Fig.  196,  A). 


Cubical  and  flat  epithelial-cells. 


Cubical  and  flat  epithelial-cells. 


%*$&m 


FIG.  196. — FROM  SECTIONS  OF  HUMAN  LUNG  (A  AND  B),  AND  (C),  OF  LUNG  of  A  KITTEN  NINE  DAYS  OLD. 
X  240.  A.  Mixed  epithelium  of  terminal  bronchiole.  B  and  C.  Alveoli  drawn  with  change  of  focus. 
The  margin  of  the  alveolus  is  shaded  ;  it  can  be  seen  that  the  epithelium  covering  it  is  like  that  in  the 
depth  of  the  alveolus  (the  light  portion) ;  the  nuclei  of  the  cells  are  not  visible.  Techn.  No.  124. 

The  epithelium  of  the  alveolar  ducts  and  of  the  alveoli  is  the  same 
as  the  respiratory  epithelium  of  the  bronchioles.  The  developmental 
history  teaches  that  the  smaller  nonnucleated  plates  originate  from 
cubical  epithelial-cells  that  become  flattened  by  inspiration,  that  is,  by  the 
inflation  of  the  alveoli  and  the  stretching  of  the  alveolar  wall.  The 
larger  plates  are  formed  by  the  subsequent  blending  of  several  smaller 
ones.  The  alveoli  of  old  embryos  and  of  stillborn  children  contain  only 
cubical  cells.  The  walls  of  the  alveolar  ducts  and  of  the  alveoli,  in  ad- 
dition to  the  previously-mentioned  muscle-fibers  in  the  former,  are  com- 
posed of  a  delicate  fibrous  framework  and  many  elastic  fibers.  The  lat- 
ter are  circularly  arranged  in  the  alveolar  ducts  ;  at  the  entrance  to  the 
alveolus  (the  base)  the  elastic  fibers  form  a  thick  annular  band  or  ring, 
while  delicate  convoluted  fibers  occur  in  the  entire  wall  of  the  alveolus. 
The  elastic  rings  of  neighboring  alveoli  grow  together  at  the  points  of 
contact  and  thus  form  the  alveolar  septa. 

The  interlobular  connective  tissue  occurring  between  the  lobules  of 
the  lungs  in  the  adult  contains,  besides  fine  elastic  fibers  and  a  few  con- 
nective-tissue cells,  black  pigment-granules  and  minutest  particles  of  car- 
bon that  have  come  there  by  inhalation.  In  children  the  interlobular 
connective  tissue  is  more  richly  developed  and  the  demarcation  of  the 
lobules  more  distinct. 


THE    RESPIRATORY    ORGANS. 


271 


The  surface  of  the  lung  is  covered  by  the  visceral  pleura ;  this  is 
composed  of  connective-tissue,  numerous  fine  elastic  fibers,  and  on  its 
free  surface  is  clothed  by  a  simple  stratum  of  flat  polygonal  epithelial- 


Elastic  rings. 


Sinuous  fibers. 


Alveolar  duct.        Alveoli.  Alveolar  septa. 

FIG.  197.— SECTION  OF  LUNG  OF  A  RABBIT.     X  220.    Staining  of  elastic  fibers.     Techn.  No.  125*. 

(endothelial)  cells.     The  parietal  pleura  has  the  same  structure,  but  con- 
tains fewer  elastic  fibers. 

The  blood-vessels  of  the  lungs,  the  branches  of  the  pulmonary  arteiy, 
enter  at  the  hilus  of  the  lung  and  run  beside  the  bronchi,  bronchioles, 
alveolar  ducts,  and  between  the 
terminal  vesicles,  where  they 
break  up  into  a  very  narrow- 
meshed  capillary  network,  that 
is  placed  immediately  beneath 
the  respiratory  epithelium  of  the 
terminal  bronchioles,  of  the  alve- 
olar ducts,  and  of  the  alveoli. 
The  veins  arise  each  at  the  base 
of  an  alveolus,  and  unite  in  small 

trunks  that  follow  the  bronchi  and  arteries.     The  walls  of  the  bronchi 
are  supplied  by  special  blood-vessels,  the  bronchial  arteries,  which  fur- 


Vein. 


Capillaries. 


_  Artery. 


FIG.  198. — FROM  A  SECTION  OF  LUNG  OF  A  CHILD, 
INJECTED  THROUGH  THE  PULMONARY  ARTERY. 
Y.  80.  Of  the  five  alveoli  drawn  the  three  upper 
ones  are  fully  injected.  Techn.  No.  126. 


2/2 


HISTOLOGY. 


nish  a  deep  capillary  plexus  for  the  muscles  and  the  glands,  a  superficial 
plexus  for  the  tunica  propria.  These  capillaries  are  taken  up  in  part  by 
the  bronchial  veins,  in  part  by  the  pulmonary  veins. 

Of  the  lymphatic  vessels  two  groups  are  recognized,  a  well-developed 
superficial  plexus  beneath  the  pleura  and  a  wide-meshed  deep  plexus  in 
the  interlobular  connective  tissue.  From  these  networks  small  stems 
furnished  with  valves  proceed,  which  follow  the  bronchi  and  emerge  at 
the  hilus,  where  they  connect  with  the  bronchial  lymph-nodules  (see 
also  p.  122). 

The  numerous  nerves  of  the  lungs,  derived  from  the  sympathetic 
and  the  vagus,  contain  medullated  and  nonmedullated  nerve-fibers  and 
small  groups  of  ganglion-cells.  The  nerve-endings  stand  chiefly  in  re- 
lation to  the  walls  of  the  blood- vessels. 

THE  THYROID  GLAND. 

The  thyroid  body  in  its  aniage  is  a  compound  tubular  gland  ;  its 
excretory  canal,  the  thy ro- glossal  duct,  opening  at  the  foramen  cecum 
of  the  tongue,  with  the  exception  of  a  few  atrophic  remains  was  oblit- 


Colloid  substance. 


Epithelium. 


Tangential  section  of 
tubule ;  the  epithe- 
lium viewed  from 
the  surface. 


Tubule  in  transverse 
section. 


Connective  tissue. 


FlG.  199.— A    LOBULK    FROM    A    THIN    SECTION   OF    THE    THYROID   GLAND    OF    ADULT    MAN.       X  22O. 

The  tubules  vary  in  diameter.  .  Techn.  No.  127. 

erated  in  an  early  embryonic  period  ;  the  network  of  gland-tubules,  that 
at  first  are  not  hollow,  becomes  constricted  at  intervals  and  resolves  itself 
into  short  pieces,  the  "follicles,"  which  become  bound  together  into 
lobules  by  loose  connective  tissue.  In  the  adult  the  tubules  are  oval 
sacs  blind  at  both  ends.  The  tubules  differ  greatly  in  diameter  (from 


THE    RESPIRATORY    ORGANS.  273 

40  fj.  to  1 20  fi)  and  are  lined  by  a  simple  layer  of  cubical  epithelial-cells. 
Their  contents  consist  of  a  characteristic,  homogeneous,  viscid  mass,  the 
colloid  substance,  which  also  is  found  in  the  lymph-vessels  of  the  organ. 
The  blood-vessels  are  exceptionally  numerous  and  break  up  into  capil- 
laries that  form  a  network  around  the  tubules,  close  beneath  the  epithe- 
lium. The  lympJiatics,  likewise  profuse,  form  a  network  lying  between 
the  tubules.  The  nerves  follow  the  ramifications  of  the  blood-vessels 
and  form  plexuses  chiefly  distributed  to  the  vascular  walls,  some  of 
which  also  surround  the  gland-tubules.  The  penetration  of  terminal 
twigs  into  the  epithelium  has  not  been  observed. 

In  the  neighborhood  of  the  thyroid  body  several  "  epithelial  cor- 
puscles," about  two  millimeters  in  size,  are  found;  they  consist  of  cords 
of  epithelial-cells,  capillary  blood-vessels,  and  connective  tissue,  and 
doubtless  are  detached  particles  of  the  lateral  anlage  of  the  thyroid  body, 
arrested  in  a  certain  stage  of  development,  which  in  circumstances  can 
become  transformed  into  the  genuine  thyroid  tissue  with  colloid  substance. 


Cortex. 


Medulla.      ^ 


Connective  tissue. 


FIG.  200. — SECTION  OF  SECONDARY  LOBUI.ES  OF  THE  THYMUS  BODY  OF  A  SEVEN-DA YS'-OLD  RABBIT. 
X  50.  The  lower  lobules  are  sectioned  tangentially,  so  that  chiefly  only  cortex  is  visible. 
Techn.  No.  128. 

THE  THYMUS  BODY. 

The  thymus  body,  in  its  first  anlage  an  epithelial  organ,  retains  this 
character  only  during  a  very  brief  embryonal  epoch,  since  with  the 
exception  of  very  small  remnants  the  epithelium  immediately  undergoes 
degeneration,  and  in  its  place  adenoid  tissue  appears.*  The  thymus  in 

*  The  adenoid  tissue  is  not  a  transformation   of  the  epithelium ;     it   originates  in   the 
embryonal  connective-tissue. 
18 


2/4  HISTOLOGY. 

childhood  consists  of  lobes  from  4  to  1 1  mm.  large,  which  are  enveloped 
by  fibrous  connective-tissue  mixed  with  fine  elastic  fibers.  This  connec- 
tive tissue  sends  septa  into  each  lobe,  by  which  a  subdivision  into  smaller 
(secondary)  lobules  I  mm.  in  size  is  effected.  Each  of  these  lobules 

consists  throughout  of  adenoid  tissue, 
which  is  more  densely  developed  at 
the  periphery  than  in  the  center,  so 
that  a  darker  cortical  zone  can  be  distin- 
guished from  a  lighter  medullary  sub- 
stance. In  the  medullary  substance 
concentrically-striated  bodies,  varying 
greatly  in  number  and  size  (from  15  to 
1 80  fj.  in  diameter)  are  found  ;  they  are 

FIG.  201.— CORPUSCLE  OF  HASSALL  FROM  * 

A  SECTION  OF  THE  THYMUS  BODY  OF      masses    of    altered    epithelial-cells    [the 

A  YOUNG  DOG.     X  50.    Techn.  No.  128. 

remains  of  the  epithelial  structures  which 

in  an  embryonic  stage  constituted  the  principal  bulk  of  the  organ]  .  They 
are  called  concentric  corpuscles  (Hassall). 

The  blood-vessels  are  very  richly  developed  and  supply  a  capillary 
system  lying  in  the  cortex  and  in  the  medulla.  The  lymphatics  likewise 
are  very  numerous  ;  the  larger  vessels  lie  on  the  surface  of  the  organ, 
their  branches  run  in  the  interlobular  septa  and  from  here  penetrate  into 
the  medullary  substance. 

At  a  later  period  the  tissue  of  the  thymus  undergoes  regressive 
change ;  the  greater  part  of  the  adenoid  structure  disappears  and  is 
replaced  by  fat. 

TECHNIC. 

No.  122. — The  Larynx,  the  Bronchi  and  the  Tliyroid  Gland. — Of 
animals,  the  cat  is  particularly  recommended.  Expose  the  bronchi  above 
the  manubrium  ;  cut  them  and  the  esophagus  through  transversely  and 
dissect  both  loose  upwards  (see  No.  97).  The  tongue  may  be  removed 
with  these  parts.  The  thyroid  gland  should  be  allowed  to  remain 
attached  to  the  larynx.  The  whole  is  to  be  placed  for  from  two  to  six 
weeks  in  200  or  400  c.c.  of  Miiller's  fluid,  then  washed  for  one  hour  in 
running  water  and  hardened  in  200  c.c.  of  gradually-strengthened 
alcohol.  In  about  eight  days  cut  sections,  transverse  and  longitudinal, 
through  the  vocal  cords  and  through  pieces  of  the  trachea  ;  stain  them  for 
five  minutes  in  Hansen's  hematoxylin  and  mount  in  damar.  Particularly 
instructive  are  sections  taken  transversely  through  the  vocal  cords,  in 
which  the  mucous  membrane,  glands,  muscles,  blood-vessels,  nerves,  and 
cartilage  furnish  material  for  the  most  varied  study. 

No.  123. —  The  Bronchi. — From  an  animal  just  killed  (rabbit) 
remove  the  lungs,  fix  them  in  Miiller's  fluid  and  harden  them  in  gradu- 


THE    RESPIRATORY    ORGANS.  2/5 

ally-strengthened  alcohol,  like  No.  122.  In  eight  days  cut  out  of  the 
lung  I  cm.  cubes  that  contain  a  portion  of  a  longitudinally-disposed 
bronchus.  With  the  scissors  remove  the  greater  part  of  the  attached 
lung  tissue  ;  embed  the  bronchus  in  liver,  and  make  thin  transverse 
sections,  which  may  be  stained  in  Hansen's  hematoxylin  and  mounted  in 
damar  (Fig.  194).  The  lungs  of  cats  are  less  suitable  than  those  of  the 
rabbit,  owing  to  the  often  considerable  masses  of  fat  surrounding  the 
bronchi.  This  method  is  also  applicable  for  the  exhibition  of  the  alveoli 
and  the  alveolar  passages. 

No.  124. — The  Respiratory  Epithelium. — For  the  demonstration  of 
this  tissue  only  animals  just  killed  can  be  used.  Young  kittens  (not 
newborn)  are  suitable  ;  they  should  be  killed  by  decapitation.  The 
trachea  and  lungs  should  be  carefully  taken  out  and  rilled  by  means  of  a 
glass  pipet  with  a  previously-prepared  solution  of  silver  nitrate  (50  c.c. 
of  a  i  per  cent,  solution  to  200  c.c.  of  distilled  water).  The  trachea 
should  then  be  tied  fast  and  the  whole  placed  for  from  one  to  twelve 
hours  in  the  remainder  of  the  silver  solution  and  stood  in  the  dark.  On 
removing  them  from  the  silver  solution,  the  lungs  should  be  quickly 
washed  with  distilled  water  and  transferred  to  150  c.c.  of  gradually- 
strengthened  alcohol,  in  which  they  may  remain  (in  the  dark)  for  an 
indefinite  length  of  time.  The  reduction  can  be  undertaken  in  an  hour 
after  the  silver  injection  or  later.  For  this  purpose  the  lungs  in  the 
alcohol  should  be  exposed  to  sunlight,  in  which  in  a  few  minutes  they 
become  a  deep  brown.  With  a  very  sharp  razor  cut  thin  sections,  taking 
care  not  to  compress  the  tissue.  Despite  the  hardening  in  alcohol  the 
lung  tissue  is  still  soft  and  allows  only  thick  sections  to  be  cut.  Sections 
may  be  most  easily  cut  in  a  direction  parallel  to  the  surface.  Place  the 
sections  for  from  ten  to  sixty  minutes  in  5  or  10  c.c.  of  distilled  water  to 
which  a  crystal  of  common  salt  about  the  size  of  a  lentil  has  been  added, 
and  mount  them  unstained  in  damar.  It  is  not  advisable  to  employ 
nuclear  staining,  since  not  only  the  nuclei  of  the  epithelial-cells,  but  also 
those  of  the  capillaries  and  other  tissues  are  colored,  and  consequently 
the  picture  becomes  very  complicated.  Orientation  in  such  cases  is  not 
•altogether  easy.  The  investigation  should  be  begun  with  the  low  power. 
The  small  alveoli  are  easily  recognized ;  the  somewhat  larger  spaces  are 
alveolar  ducts.  The  demarcation  of  the  epithelium  is  on  the  whole  finer 
with  medium  magnification  (80  diameters),  and  by  no  means  equally 
good  in  all  places.  The  cubical  epithelial-cells  are  usually  colored  a 
somewhat  deeper  brown.  Find  a  good  place,  study  it  with  the  high 
power  (240  diameters),  and  by  changing  the  focus  (elevating  and  depress- 
ing the  tube)  note  the  relief  of  the  preparation  ;  with  high  magnification, 
either  only  the  interior  or  the  margin  of  an  alveolus  can  be  distinctly 
seen.  Fig.  196  was  drawn  with  change  of  focus.  The  pores  of  the 
alveoli  can  be  shown  only  by  careful  injection  of  lungs  that  have  been 
made  empty  of  air. 

No.    125. — Elastic   Fibers    of    the    Lungs. — (a)  Fresh. — With    the 
scissors  placed  on  a  freshly-cut  surface  of  the  lung  (the  lung  need  not 


HISTOLOGY. 

be  fresh),  cut  a  flat  piece  about  I  cm.  square,  spread  it  out  with  needles 
on  a  dry  slide,  apply  a  cover-glass  and  treat  with  two  drops  of  potash 
lye  diluted  one-half  with  water ;  the  diluted  lye  destroys  all  parts 
excepting  only  the  elastic  fibers,  the  thickness  and  arrangement  of  which 
may  be  easily  investigated  with  the  high  power  (240  diameters). 

(&)  Permanent  Preparation. — Fix  i  or  2  cm.  cubes  of  lung  in  abso- 
lute alcohol  (§  4,  p.  30)  for  forty-eight  hours,  stain  thick  sections  in 
orcein  (p.  40)  and  mount  in  damar  (Fig.  197). 

No.  126. — Blood-vessels  of  the  Lungs. — Inject  the  lung  from  the 
pulmonary  artery  with  Berlin  blue  ;  fix  it  in  Muller's  fluid,  and  harden 
it  in  alcohol.  Cut  thick  sections,  principally  parallel  to  the  surface  of 
the  lung  (Fig.  198). 

No.  127. — The  Thyroid  Gland. — Thin  sections  of  the  gland,  har- 
dened in  toto  (see  No.  122),  are  to  be  stained  with  picrocarmine  and 
mounted  in  damar  (Fig.  199).  The  retracted  colloid  masses  stain  an  in- 
tense yellow.  Examine  thick  sections  in  glycerol,  in  which  the  lymph- 
vessels  filled  with  colloid  substance  are  often  distinctly  visible. 

No.  128. —  The  Thymus  Body. — Place  the  thymus  body  of  a  young 
animal  in  Muller's  fluid  for  from  two  to  five  weeks  and  harden  it  in 
gradually-strengthened  alcohol.  Stain  sections  with  Hansen's  hema- 
toxylin  ;  mount  them  in  damar  (Fig.  200).  Care  should  be  taken  not 
to  confuse  the  cross-sections  of  the  blood-vessels,  the  lumina  of  which 
change  in  elevating  and  depressing  the  tube  (when  they  are  not  true 
cross-sections),  with  the  concentrically-striated  corpuscles  of  Hassall. 
The  preparation  represented  in  Fig.  201  is  from  a  thymus  body  fixed  in 
Flemming's  mixture  and  stained  with  safranin. 


VIII.  THE  URINARY  ORGANS. 

THE  KIDNEYS. 

The  kidneys  are  compound  tubular  glands,  which  exclusively 
consist  of  minute  tubes,  the  uriniferous  tubules.  The  macroscopically 
perceptible  differences  between  the  peripheral  and  central  portions  of  the 
organ,  the  so-called  cortical  and  medullary  regions,  are  principally  deter- 
mined by  the  course  of  the  uriniferous  tubules,  the  divisions  within  the 
cortex  pursuing  a  tortuous,  those  within  the  medulla  a  straight  course. 

Each  uriniferous  tubule  begins  in  the  cortex  as  a  spherical  dilata- 
tion, renal  corpuscle  (Malpighi),  which  is  marked  off  by  a  constriction, 
the  neck,  from  the  greatly-convoluted  succeeding  division,  the  proxi- 
mal convoluted  tubule.  This  passes  into  a  straight  portion,  that  is  at  first 
centrally  directed,  but  soon  turns  back  and  forms  a  loop,  Henle's  loop, 
in  which  a  descending  and  an  ascending  limb  may  be  distinguished.  The 
latter  passes  into  a  convoluted  portion,  the  intercalated  or  distal  convo- 
luted tubule  (spiral  tubule),  that  as  it  proceeds  takes  a  straight  course 
and  is  then  called  collecting  tubule  (Fig.  202).  The  collecting  tubules, 
during  their  centrally-directed  course,  take  up  other  distal  convoluted 
tubules,  unite  under  acute  angles  with  neighboring  collecting  tubules, 
and  converge  toward  the  apex  of  a  renal  papilla,  where,  diminished  in 
number  but  greatly  increased  in  diameter,  they  terminate  in  \h^  papillary 
duct.  Henle's  loop-tubules  and  the  collecting  tubules  are  named  straight 
tubules  (tubuli  recti).  Each  uriniferous  tubule  pursues  a  completely  iso- 
lated course  until  it  is  taken  up  by  a  collecting  tubule.  The  loops  of 
Henle  and  the  peripheral  portions  of  the  collecting  tubules  are  grouped 
together  as  they  pass  toward  the  medulla  and  form  the  structures  in  the 
cortex  known  as  medullary  rays  or  pyramids  of  Ferrein. 

The  minute  structure  of  the  uriniferous  tubules  differs  so  greatly 
in  the  several  divisions  that  a  separate  consideration  of  each  division  is 
necessary.  The  renal ^  corpuscles  (Malpighi),  from  0.13  to  0.22  mm.  in 
size,  consist  of  a  spherical  plexus  of  blood-vessels,  the  glomerulus,  and  the 
expanded  and  invaginated  blind  initial  extremity  of  a  uriniferous  tubule, 
the  capsule  of  the  glomerulus  (Bowman).  The  glomerulus  lies  within 
the  invaginated  portion  of  the  capsule,  and  is  almost  completely  envel- 

277 


2/8  HISTOLOGY. 

oped  by  it.     Accordingly,  two  layers  are  distinguished  in  the  capsule,  an 
inner  (quasi   visceral)   lying  close  upon  the  glomerulus,   and  an  outer 


FIG.  202. —  SCHEME  OF  THE  COURSE  OF  THE 
URINIFEROUS  TUBULES  (LEFT)  AND  OF  THE 
RENAL  BLOOD-VESSELS  (RIGHT),  sketched 
from  a  section  of  kidney  of  an  infant  seven 
weeks  old.  X  10.  R.  Cortex.  M.  Medulla. 
m.  s  ,  Medullary  rays,  /j,  /2,  /3,  Three  renal 
lobules.  «,  Renal  ""corpuscle  ;  d,  proximal  con- 
voluted tubule;  c,  descending,  d,  ascending 
limb  of  Henle's  loop-tube;  e,  distal  convoluted 
tubule  (spiral  tubule);  /".collecting  tubule;  f\, 
portions  of  collecting  tubules  ;  g,  excretory  duct, 
i.  Branch  of  renal  artery.  2.  Interlobular  artery. 
3.  Afferent  artery.  4.  Efferent  artery.  5.  Inter- 
lobular vein.  6.  Branch  of  renal  vein,  x  and 
xx,  Branches  supplying  the  medulla. 


y 


FIG.  203.— ISOLATED  URINIFEROUS  TUBULES  OF 
A  FOUR-WEEKS'-OLD  RABBIT.  X  30.  a,  Mal- 
pighian  corpuscle.  b,  Proximal  convoluted 
tubule,  c,  Henle's  loop,  descending  limb  ;  d, 
ascending  limb.  ./",  Collecting  tubule,  g,  Papil- 
lary duct.  Techn.  No.  129. 


(quasi  parietal)  layer ;  the  former,  in  young  animals,  is  composed  of 
cubical  cells,  that  later  become  more  and  more  flattened,  the  latter  of  flat 
polygonal  cells  (Fig.  205). 


THE    URINARY    ORGANS. 


279 


At  the  neck  of  the  capsule   the  outer  layer  passes  over  into  the 
walls  of  the  proximal  convoluted  tubule,   which  is  from  40  to  60  /*  thick. 


Proximal  convoluted  tubule. 


Straight  collecting  tubule. 


Cortex. 


Medulla. 


ait 


Renal  corpuscle. 


Medullary  ray. 


Arterv. 


Vein. 


Running  at  the 
boundary  between 
the  cortex  and 
medulla  (Cf.  Fig. 
202). 


Blood-vessels. 


~~~-    Henle's  loop. 


FIG.  204.— FROM  A  SECTION  OF  HUMAN  KIDNEY,  INCLUDING  A  PORTION  OF  THE  CORTEX  AND  THE 
MEDULLA.    At  x  two  renal  corpuscles  have  fallen  out.     X  20.    Techn.  No.  130. 

The   protoplasm  of  the  cells  of  this   division,  the  boundaries  of  which 
are   not  sharply  defined,   consists  of  granules  that  by  means  of  proto- 


Afferent  artery. 


Efferent  artery. 


Bowman's  capsule. 


[£}  Uriniferous  tubule. 


FIG.  205. — SCHEME.  On  the  left  is  an  artery 
that  on  the  right  gives  off  an  afferent 
vessel;  this  breaks  up  into  branches, 
which  turn  into  the  radicles  of  the  effer- 
ent vessel(directed  toward  the  right).  The 
three  loops  are  intended  to  represent  the 
glomerulus;  this  lies  in  Bowman's  cap- 
sule, of  which  both  layers  are  visible ; 
below,  the  capsule  passes  into  the  urini- 
ferous  tubule. 


Efferent  artery  (or 
afferent?-) 


Glomerulus. 


—  Capsule  (outer  layer). 


—  Beginning  of  urinif- 
erous  tubule. 


FIG.  206.— FROM  A  SECTION  THROUGH  THE  CORTEX  OF 
THE  KIDNEY  OF  A  MOUSE,  SHOWING  THE  CONNECTION 
BETWEEN  BOWMAN'S  CAPSULE  AND  THE  URINIFEROUS 
TUBULE.  X  240. 


plasmic   filaments  are  bound  together   in   rows  radially    placed   to  the 
lumen  ;  these  rows  are  most  distinctly  seen  at  the  base  of  the  cell  and 


28O  HISTOLOGY. 

with  medium  magnification  have  the  appearance  of  minute  rods  (Fig. 
207).  The  nuclei  of  the  cells  always  lie  near  the  base  ;  the  surface  of 

the  cell  that  is  directed  toward  the  lumen 
&      .  is  in   some  places    provided   with    an    ex- 

^SBlfev  tremely  unstable   striated    border  (p.   66), 

A  ;-g  the  "brush-border." 

-:d^  The  descending  limb  of  Henle's  loop 

fm  is  from  9  to  I  5  p.  thick  ;  the  lumen  is  very 

p^  wide.      It  is  lined  by  squamous  epithelial- 

FIG.  207.— A.    ISOLATED    CELL    OF    A  Cells,     the    nuclei     of    which '  often    protrude 
PROXIMAL     CONVOLUTED     TUBULE. 

The  base  of  the  cell  is  separated  into  mtO  the    lumen   (Fig;.    2OQ).        The  aSCCndill°~ 
minute  rods.     B.  Transverse  section  x 

of  a  proximal  convoluted  tubule;  the  //,;/£    Js    from     2  3     to     28   P-  thick,  the    lumen 
rods  appear  as  delicate  stria;.     Both  J 

x^o^Techn^o^.^    kidney-      relatively    narrower.       The    epithelial-cells 

resemble  those  of  the  convoluted  divisions, 

but  are  somewhat  lower  (Fig.  209).  The  transition  of  the  narrow 
descending  limb  into  the  thicker  ascending  portion  does  not  always  occur 
at  the  loop.  The  intercalated  or  distal  convoluted  portion  (spiral  tubule) 
is  from  39  to  46  ,«  thick ;  the  epithelial-cells  are  cylindrical  or  conical  in 
shape  and  have  a  peculiar  luster.  The  collecting  tubides  in  crease  in  thick- 
ness as  they  approach  the  apex  of  the  papilla ;  the  thinnest  have  a  diam- 
eter of  45  AI,  the  thickest  (the  papillary  duct)  a  diameter  of  from  200  to 
300  />-.  Their  epithelial-cells  are  in  part  clear,  in  part  granular  columnar 
elements,  that  increase  in  height  with  the  increase  of  the  diameter  of  the 
tubule  (Fig.  209). 

The  uriniferous  tubules  are  covered  in  their  entire  length  by  a  struc- 
tureless membrana  propria  situated  outside  of  the  epithelium,  which  is 
thickest  in  the  descending  limb  of  Henle's  loop.  The  tubules  are  envel- 
oped by  a  small  amount  of  loose  connective  tissue  (interstitial  connective 
tissue),  which  on  the  surface  of  the  kidney  is  condensed  and  forms  a 
fibrous  investment  (tunica  albuginea)  containing  smooth  muscle-fibers. 
The  blood-vessels  run  in  the  interstitial  connective  tissue. 

The  blood-vessels  of  tlie  kidneys.  The  renal  artery  divides  in  the 
hilus  of  the  kidney  into  branches,  the  interlobular  arteries  (artcrice  intcr- 
lobares),  which  after  giving  off  small  twigs  to  the  capsule  and  to  the  calices 
of  the  kidney  enter  the  parenchyma  of  the  organ  at  the  circumference  of 
the  papillae  and  without  branching  pass  to  the  boundary  between  the 
cortex  and  the  medulla  (Fig.  202).  Here  the  arteries  bend  at  right  angles 
and  form  arches  (arterice  arciformes)  along  the  boundary  line,  with  the 
convexity  toward  the  periphery.  From  the  convex  side  of  the  arches, 
and  from  their  terminal  ramifications,  at  regular  intervals  spring  branches 


Bowman's  capsule. 
\ 


Glomerulus. 
/ 


"?•  '    *''          ' 


Distal  convo-  /• 
luted  tubule 
(spiral     tu- 
bule). 


Capillary. 
Henle's  tubule.  / 

Small  collecting  tubule. 

FIG  208.— FROM  A  SECTION  THROUGH  THE  CORTEX  OF  A  HUMAN  KIDNEY  (parallel  to  the  surface).    At 
the  left  lower  corner  there  is  a  cross-sectioned  medullary  ray.     X  200.    (Schaper.)    Techn.  No.  130. 


Large  collecting 
tubule. 


X 


,.>>(•§£?#* 


Capillary. ' 


Ascendinglimbol 
Henle's  loop. 


Descending   limb 
of  Heule's  loop. 


FIG.  209.— FROM  A  TRANSVERSE  SECTION  THROUGH  THE  MEDULLA  OF  A  HUMAN  KIDNEY.    X  320. 

(Schaper.)    Techn.  No.  130. 


282 


HISTOLOGY. 


running  toward  the  periphery,  the  interlobidar  arteries  *  (arteriae  inter- 
lobulares),  which  give  off  short  lateral  twigs,  each  of  which  supplies  a 
glomerulus  (Fig.  202,  2,  and  Fig.  210).  Each  interlobular  artery  breaks 
up  into  terminal  branches,  that  in  part  supply  the  capsule,  in  part  continue 
as  the  capillaries  of  the  cortex  or  form  the  afferent  vessel  (Fig.  202,  3)  of 
a  glomerulus.  Each  glomerulus  arises  by  the  rapid  division  of  the 
afferent  artery  into  a  number  of  small  twigs,  that  immediately  reunite  in  a 
single  arterial  vessel, f  called  the  efferent  artery,  which  is  somewhat 
smaller  than  the  entering  vessel  (Fig.  202,  4,  and  Fig.  210).  The  efferent 


Capillary  network   of  cortex  with 
round  meshes. 


-    Interlobular  vein. 
Interlobular  artery. 


n 

&%.i —    Afferent  vessel. 


-    Efferent  vessel. 

Capillary  network  of  a  medullary 

ray  with  elongated  meshes. 


FIG.  210.— FROM  A  LONGITUDINAL  SECTION  OF  THE  INJECTED  KIDNEY  OF  A  GUINEA-PIG.    X  30. 

Techn.  No.  133. 

artery  breaks  up  into  a  capillary  networl^with  round  meshes  in  the  region 
of  the  convoluted  tubules,  with  elongated  meshes  in  the  region  of  the 
medullary  rays.  From  the  latter  veins  arise,  the  interlobular  veins  (venae 
interlobulares),  which  lie  close  beside  the  interlobular  arteries,  retrace  the 
course  of  the  arteries,  and  open  into  the  venae  arciformes  ;  the  latter  also 
take  up  small  veins  that  arise  from  the  confluence  of  capillaries  situated 


*  Microscopic  regions  of  the  kidney  with  ill-defined  boundaries,  in  the  axis  of  which  lies 
a  medullary  ray  and  at  the  periphery  of  which  interlobular  arteries  ascend,  are  designated  lob- 
ules. In  Fig.  202  three  lobules,  /lf  /2,  /3,  are  indicated  by  dotted  lines.  These  lobules  have 
no  relation  whatever  to  the  lobules  of  the  kidney  during  fetal  life. 

f  Consequently  each  glomerulus  is  an  arterial  rete  mirabile  (see  p.  122).  In  dogs  and  cats 
retia  mirabilia  occur  in  the  kidneys  that  do  not  stand  in  any  relation  to  uriniferous  tubules,  that 
is,  they  are  not  enveloped  in  a  capsule. 


THE    URINARY    ORGANS. 


283 


in  the  deeper  portions  of  the  cortex.  The  vessels  of  the  peripheral  zone 
of  the  cortex  converge  to  points  where  they  unite  in  radicles  arranged 
in  a  stellate  form,  the  vence  stellatcz,  which  join  the  interlobular  veins 
(Fig.  202,  5,  and  Fig.  210).  The  foregoing  account  of  the  distribution 
of  the  blood-vessels  applies  only  to  the  cortex  and  to  the  medullary 
rays. 

The  medulla  receives  its  blood  supply  from  (i)  the  artcriolce  recta, 
which  arise  from  the  arterial  arches  at  the  juncture  of  the  medulla  and  the 
cortex,  from  the  efferent  vessels  of  the  most  deeply-situated  glomeruli,  and 
direct  from  centrally-running  branches  of  the  interlobular  arteries  or  of  the 
arciform  arteries  ;  and  (2)  from  offshoots  of  the  cortical  capillaries  (Fig.  202, 
x,  xx).  The  veins  of  the  medulla  take  their  origin  from  the  wide-meshed 


Renal  corpuscle. 


Nerve  plexus  of  an  interlobular  artery. 


Silvered  uriniferous  tubule. 
FIG.  211. — SECTION  OF  THE  KIDNEY  OF  A  MOUSE.    X  180.    Techn.  No.  134. 

capillary  network  surrounding  the  papillary  ducts  and  join  the  venous 
arches  at  the  juncture  of  the  medulla  and  the  cortex.  The  renal  vein 
and  its  branches  have  no  valves.  Direct  communications  between  the 
arteries  and  veins  occur  both  in  the  capsule  and  in  the  interior  of  the 
kidney. 

The  lymph-vessels  run  in  part  superficially,  in  the  capsule,  and  in  part 
accompany  the  arteries  in  the  parenchyma  of  the  organ.  The  nerves 
form  plexuses  which  envelop  the  arteries  as  far  as  the  renal  corpuscles 
(Fig.  2 1 1).  The  convoluted  uriniferous  tubules  are  said  to  be  surrounded 
by  nerve-fibers,  extremely  delicate  branches  of  which  pierce  the  mem- 
brana  propria  and  terminate  in  free  endings  between  the  epithelial-cells. 


284 


HISTOLOGY. 


THE  URETERS. 

The  ureters,  the  calices,  and  the  pelvis  of  the  kidney  are  composed 
of  three  coats,  (i)  the  mucous  coat,  which  lies  innermost,  (2)  the  muscular 
coat,  and  (3)  surrounding  this  the  outer  fibrous  coat  (Fig.  212). 


Fibrous  coat. 


Muscular  coat. 


Mucous  coat. 


^^.K^/V'  &$3^%40?# 


FIG.  212. — TRANSVERSE  SECTION  OF  THE  LOWER  HALF  OF  A  HUMAN  URETER.  X  15.  e,  Epithelium ; 
t,  tunica  propria  ;  s,  submucosa;  /,  inner  longitudinal  muscle-bundles;  r,  circular  layer  of  muscle- 
bundles ;  /!,  accessory  outer  longitudinal  muscle-bundles.  Techn.  No.  135. 

The  tunica  propria  of  the  mucous  membrane  consists   of  delicate 
connective-tissue  fibers,  which,  richly  interspersed  with  cellular  elements, 


Columnar  cells. 


Leucocyte. 


__  Tunica  propria. 


FIG.  213. — PORTION  OF  A  VERTICAL  SECTION  OF  A  HUMAN  VESICAL  Mucous  MEMBRANE.    X  560. 

Techn.  No.  136. 

pass  without  sharp  demarcation  into  the  tissue  of  the  submucosa.     The 
epithelium    covering   the    tunica   propria  is  the   so-called   "  transitional 


THE    URINARY    ORGANS.  285 

epithelium  "  ;  that  is,  a  stratified  scaly  epithelium  composed  of  but  few 
layers,  of  which  the  uppermost  layer  consists  of  cylindrical  or  cubical, 
only  slightly-flattened  elements.  Occasionally,  instead  of  the  latter,  large 
plate-like  cells  are  present,  which  contain  several  nuclei  that  have  arisen 
by  amitotic  division  (p.  60,  remark  f). 

The  muscular  coat  consists  of  an  inner  longitudinal  and  an  outer 
circular  layer  of  smooth  muscle-fibers,  which  in  the  lower  half  of  the 
ureter  possesses  an  additional  discontinuous  outer  layer  of  longitudinally- 
arranged  muscle-bundles. 

The  fibrous  coat  consists  of  loosely-united  connective-tissue  bundles. 

The  mucous  membrane  of  the  calices  is  continued  over  the  surface 
of  the  renal  papillae,  the  circular  muscle-fibers  form  a  sphincter  muscle 
around  the  papillae. 

The  blood-  and  the  lympli-vessels  are  especially  numerous  in  the 
mucous  coat.  The  nerves  are  principally  distributed  to  the  muscular 
coat ;  single  fibers  extend  into  the  tunica  propria  as  far  as  the  epithelium. 


THE  URINARY  BLADDER, 

The  urinary  bladder  likewise  consists  of  a  mucous,  a  muscular,  and 
a  fibrous  coat.  The  epithelium  resembles  that  of  the  ureter  and  the 
pelvis  of  the  kidney  in  every  particular ;  a  distinction  from  these  is 
impossible.  The  tunica  propria  occasionally  contains  solitary  lymph- 
nodules.  The  muscular  coat  consists  of  strata  of  smooth  muscle-fibers, 
an  inner  and  an  outer  longitudinal  layer,  which  enclose  between  them  a 
circular  layer.  The  layers  interlace  in  such  a  manner  that  it  is  not 
possible  to  define  their  exact  limits.  At  the  base  of  the  bladder  the  inner 
longitudinal  layer  is  augmented,  the  circular  layer  forms  the  not  always 
distinct  internal  vesical  sphincter.  Blood-  and  lymph-vessels  comport 
themselves  as  in  the  ureter ;  microscopic  groups  of  ganglion-cells  are 
situated  along  the  course  of  the  nerves. 

In  the  tunica  propria  of  the  lower  division  of  the  pelvis  of  the 
kidney,  of  the  upper  portion  of  the  ureter,  and  of  the  bladder  round  or  oval 
bodies  occur,  that  have  been  erroneously  regarded  as  glands.  They  are 
sprouts  of  the  surface  epithelium,  possess  the  same  structure,  are  without 
a  lumen,  and  occasionally  even  have  severed  their  connection  with  the 
superficial  epithelium. 

THE  URETHRA. 

The  female  urethra  is  composed  of  a  mucous  coat  and  a  robust 
muscular  coat.  The  tunica  propria  consists  of  delicate  fibrous  connective 


286  HISTOLOGY. 

tissue  containing  numerous  connective-tissue  cells  and  is  elevated  in 
numerous  papillae,  that  are  especially  well  developed  near  the  meatus. 
The  epithelium  varies,  in  some  individuals  it  is  a  stratified  scaly,  in  others 
a  simple  columnar  epithelium.  A  few  branched  simple  tubular  glands 
are  present ;  they  occur  in  small  groups  at  the  meatus  and  are  called 
"  periurethral  "  glands.  The  muscular  coat  consists  of  an  inner  longi- 
tudinal and  an  outer  circular  layer  of  nonstriped  muscle-fibers,  between 
which  extends  a  compact  fibrous  connective  tissue  containing  many 
elastic  fibers.  The  mucous  coat  is  richly  supplied  with  veins,  the  net- 
works of  which  extend  into  the  longitudinal  layer  of  the  muscular  coat ; 
in  this  way  a  structure  similar  to  the  corpus  cavernosum  of  the  male 
urethra,  the  corpus  spongiosum,  is  formed. 

The  male  urethra  (better,  male  urogenital  sinus)  is  likewise  composed 
of  a  mucous  coat  and  a  muscular  coat,  but  they  vary  in  structure  in  the 
different  parts  of  the  canal.  In  the  prostatic  portion  the  epithelium 
resembles  that  of  the  bladder ;  in  the  membranous  division  it  gradually 
passes  into  the  stratified  columnar  variety,  which  in  the  spongy  part  is 
transformed  to  a  simple  columnar  epithelium.  From  the  fossa  navicu- 
laris  on,  the  epithelium  is  of  the  stratified  squamous  type.  The  tunica 
propria  is  rich  in  elastic  fibers  and  is  beset  with  papillae,  that  are  especially 
well  developed  in  the  fossa  navicularis.  Isolated  branched  simple  tubular 
glands,  the  urethral  glands  (glandules  urethrales,  Litrii),  occur  through- 
out the  entire  urethra.  The  muscular  coat  in  the  prostatic  division 
consists  of  an  inner  longitudinal  and  an  outer  circular  layer  of  smooth 
muscle-fibers ;  both  layers  are  still  well  defined  in  the  membranous 
portion,  but  gradually  cease  in  the  spongy  portion,  where  the  circular 
layer,  still  conspicuous  in  the  bulbus  urethrae,  is  the  first  to  disappear ; 
in  the  anterior  part  of  the  spongy  division  a  few  oblique  and  longitudinal 
bundles  occur  (Fig.  221).  The  mucous  membrane  has  a  rich  vascular 
supply  (see  corpus  cavernosum  urethrae,  p.  297).  The  lymph-vessels  lie 
beneath  the  blood-vessels. 

TECHNIC. 

No.  129. — Isolated  Uriniferous  Tubules. — The  most  suitable  for  this 
purpose  are  the  kidneys  of  young  animals,  for  example  newborn  kittens. 
Divide  the  kidney  in  halves  ;  place  one  half  (a)  aside  for  investigation 
fresh  ;  cut  the  other  half  (b)  into  pieces  including  the  cortex  and  medulla, 
and  place  them  in  30  c.c.  of  pure  hydrochloric  acid. 

a.  Tease  a  pea-sized  piece  in  a  drop  of  0.75  per  cent,  salt  solution. 
The  red  glomeruli,  the  convoluted  and  straight  uriniferous  tubules,  can 
be  seen  with  the  low  power.  The  convoluted  tubules  are  dark  and 
granular,  the  other  divisions  clear.  With  high  magnification,  the  nuclei 


THE    URINARY    ORGANS.  28/ 

of  the  clear  portion  of  the  uriniferous  tubules  can  be  distinctly  seen  ;  the 
cell  boundaries  may  best  be  seen  in  the  collecting  tubules.  In  the  con- 
voluted tubules  only  the  fine  striation  of  the  bases  of  the  gland-cells  can 
be  seen  ;  cell  boundaries  and  nuclei  are  not  visible. 

b.  In  about  two  hours  the  red  pieces  of  kidney  tissue  should  be 
transferred  to  a  capsule  containing  50  c.c.  of  distilled  water,  in  which 
they  rapidly  turn  a  dirty  gray  and  acquire  smeary  surfaces.  The  water 
is  to  be  changed.  After  a  few  moments  small  pieces  can  be  detached 
with  needles  and  readily  separated  into  tubules,  in  a  little  water  on  a 
slide.  If  it  is  desired  to  obtain  entire  uriniferous  tubules,  transfer  pieces 
of  kidney  2  cm.  square  to  a  watch-glass  in  which  has  been  placed  a 
cover-glass  and  enough  distilled  water  to  cover  the  surface  of  the  latter. 
The  tubules  should  now  be  isolated  with  needles.  If  the  isolation  is 
successful — this  may  be  ascertained  by  examination  with  the  low  power 
— with  filter-paper  carefully  absorb  the  water  from  the  watch-glass  and 
then  from  the  cover-glass,  take  out  the  latter,  cleanse  its  free  surface,  and 
place  it  with  the  attached  tubules  gently  on  a  slide  on  which  a  drop  of 
dilute  glycerol  has  been  previously  placed.  The  preparation  may  be 
subsequently  stained  under  the  cover-glass  with  picrocarmine  (Fig.  203). 

No.  1 30. — The  Cortex  and  Medulla. — For  sections,  the  kitten's  other 
kidney  or  other  pieces  of  kidney  tissue  2  or  3  cm.  square  are  to  be  fixed  in 
200  or  300  c.c.  of  Miiller's  fluid  for  four  weeks,  or  in  Zenker's  fluid  for 
forty-eight  hours,  and  hardened  in  100  c.c.  of  gradually-strengthened 
alcohol.  Fixation  in  absolute  alcohol  (like  No.  132)  is  still  better.  Thick 
transverse  and  longitudinal  sections  through  the  cortex  and  similar  ones 
through  the  medulla  are  to  be  examined  unstained  in  dilute  glycerol, 
with  a  low  power.  Thin  transverse  sections  through  the  apex  of  the 
papillae  for  the  excretory  duct,  through  the  base  of  the  papillae  (Fig. 
209),  and  through  the  cortex  are  to  be  stained  with  Hansen's  hema- 
toxylin  and  mounted  in  damar.  Endeavor  to  cut  radial  sections  through 
the  cortex  and  the  medulla,  showing  the  boundary  between  the  two  ; 
examine  them  unstained  in  glycerol,  with  the  low  power.  Frequently 
the  blood-vessels  are  still  filled  with  blood-corpuscles  and  may  be  traced 
for  long  distances.  The  extremely  delicate  "brush-borders"  can  be 
seen  only  here  and  there,  with  very  high  magnification.  Frequently  they 
have  fallen  off. 

No.  131. — Medullary  rays  and  Henle's  loops  are  especially  fine  in 
stained  vertical  sections  of  the  kidneys  of  young  animals  prepared  after 
No.  130. 

No.  132. — For  the  study  of  the  glomeruli  and  Boivman's  capsule, 
also  the  connection  of  the  latter  with  the  uriniferous  tubule,  the 
kidney  of  the  mouse  is  most  suitable.  Fix  and  harden  the  divided 
kidney  in  15  c.c.  of  absolute  alcohol,  which  should  be  changed  in  an 
hour.  After  three  days  (or  later)  cut  thin  sections  of  the  cortex,  stain 
them  two  or  three  minutes  in  Hansen's  hematoxylin  and  mount  in  damar 
(Fig.  206).  The  invaginated  portion  of  the  capsule,  on  account  of  the 
similarly-stained  nuclei  of  the  blood-vessel  walls,  cannot  be  distinguished. 


288  HISTOLOGY. 

No.  133. — The  Blood-vessels  of  the  Kidney. — An  isolated  kidney  may 
be  injected  (p.  43)  and  fixed  in  300  c.c.  of  Miiller's  fluid  for  four  weeks 
and  then  hardened  in  150  c.c.  of  gradually-strengthened  alcohol.  The 
venae  stellatae  can  be  investigated  macroscopically.  Unstained  thick 
longitudinal  and  transverse  sections  should  be  studied  with  the  low  power 
(Fig.  210). 

No.  134. — Nerves  of  the  Kidney. — Treat  small  pieces  according  to 
Golgi's  method  given  on  p.  41  ;  they  should  remain  from  three  to  six 
days  in  the  osmiobichromate  mixture. 

No.  135. — The  Pelvis  of  the  Kidney  and  the  Ureters. — Of  the  former 
pieces  I  cm.  square,  of  the  latter  I  or  2  cm.  long  should  be  fixed  in 
Muller's  fluid  and  in  fourteen  days  hardened  in  100  c.c.  of  gradually- 
strengthened  alcohol.  Stain  sections  with  Hansen's  hematoxylin  and 
mount  in  damar. 

No.  136. — Treat  the  Bladder  like  No.  135. 

No.  137. — Epithelial  Cells  of  the  Pelvis  of  the  Kidney,  of  the  Ureter, 
and  of  the  Bladder. — Place  pieces  of  these  parts,  I  cm.  square  (cut  open 
the  ureter),  in  30  c.c.  of  Ranvier's  alcohol  (p.  20).  Isolate  and  stain 
with  picrocarmine  (p.  38).  Mount  in  diluted  acidulated  glycerol  (p.  48). 

No.  138. — The  Female  Urethra. — Cut  out  a  piece  of  the  female 
urethra  about  2  cm.  long,  together  with  the  attached  anterior  vaginal 
wall;  place  it  in  100  or  200  c.c.  of  Muller's  fluid  for  fixation,  and  in 
two  or  three  weeks  harden  it  in  gradually-strengthened  alcohol  (p.  33). 
Stain  cross-sections  in  Hansen's  hematoxylin  (p.  36)  and  mount  in  damar 

(P-  45)- 

No.  139. — The  Male  Urethra. — Treat  pieces  I  or  3  cm.  long  of  the 
prostatic,  membranous,  and  cavernous  portions  and  of  the  fossa  navic- 
ularis  like  No.  138.  Care  should  be  exercised  not  to  confuse  the 
urethral  lacunae  (Morgagni),  blind  evaginations  of  the  mucosa,  with 
sections  of  glands. 


IX.    THE  REPRODUCTIVE  ORGANS. 

THE    MALE    REPRODUCTIVE    ORGANS. 

THE  TESTICLE. 

The  testicles  are  glands  consisting  of  branched,  pouch-like  tubules, 
the  seminiferous  tubules,  which  are  enveloped  in  a  connective-tissue  cap- 
sule. This  capsule,  the  tunica  albuginea,  is  a  tough  membrane,  which 
encloses  the  parenchyma  on  all  sides  and  on  the  posterior  upper  aspect  is 
thickened,  forming  a  mass,  the  mediastinum  testis  (corpus  Highmori),  which 
juts  into  the  interior  of  the  organ.  From  this  a  number  of  septa  arise, 
which  pass  along  divergent  paths  to  the  tunica  albuginea  and  so  divide 
the  parenchyma  of  the  testicle  into  pyramidal  lobules,  the  base  of  which 
is  directed  toward  the  capsule,  the  apex  toward  the  corpus  Highmori. 
The  tunica  albuginea  consists  of  dense  fibrous  connective  tissue,  which 
on  its  free  surface  is  covered  by  a  simple  layer  of  flat  epithelial-cells,* 
on  its  inner  surface  is  in  contact  with  a  layer  of  loose  connective  tissue  ; 
this  supports  numerous  blood-vessels  and  is  called  tunica  vasculosa ;  it 
is  connected  with  the  interlobular  septa.  The  mediastinum,  a  dense 
connective-tissue  structure,  contains  a  network  of  freely-anastomosing 
tubules,  the  rete  testis  (Haller).  The  interlobular  septa  consist  of 
bundles  of  connective  tissue,  continuous  with  the  connective  tissue  sur- 
rounding the  individual  seminiferous  tubules.  This  "interstitial"  con- 
nective tissue  is  rich  in  cellular  elements,  which  are  in  part  flat 
connective-tissue  cells,  in  part  spherical  cells,  the  so-called  interstitial 
cells,  containing  pigment  or  fatty  granules,  in  man  also  crystalloids. 

The  seminiferous  tubules  in  their  course  may  be  divided  into  three 
portions  :  they  begin  as  (i)  the  convoluted  tubules,  which  pass  into  (2)  the 
straight  tubules,  which  continue  as  (3)  the  rete  testis.  The  convoluted 
tubules  are  round,  winding  canals,  about  140  /*  in  diameter,  of  which  the 
initial  extremity  has  not  yet  been  definitely  located  ;  probably  they  are 
united  with  one  another  at  the  periphery,  beneath  the  tunica  vasculosa, 
and  so  form  a  network  from  which  numerous  tubules  turn  aside  and  with 

*This  is  the  visceral  layer  of  the  tunica  vaginalis  propria. 
'9  289 


290 


HISTOLOGY. 


many  windings  pass  toward  the  mediastinum.     Tubules  with  blind  ends 
have  been  observed.      During  their  course  the  tubules  diminish  in  number, 


ti 

' 


Ductus  defer- 
ens. 


-  Blood-vessels. 


Epididymis. 


Mediastinum  con- 
taining the  rete 
testis. 

Straight 

tubules. 


^ ^  Septa. 


Lobules  con- 
sisting of  con- 
voluted tubules 


Tunica  vascu- 

losa. 

Tunica  albu- 
ginea. 


FIG.  214.— CROSS-SECTION  OF  THE  TESTICLE  OF  A  NEWBORN  CHILD.    X  10.    Techn.  No.  140. 


Developing 

seminal 

filaments. 


Interstitial  con- 
nective tissues.       S 


Epithelium  in  a 
state  of  ac- 
tivity. 


Epithelium  in  a 
state  of  rest. 


FIG.  215.— FROM  A  CROSS-SECTION  OF  THE  TESTICLE  OF  AN. Ox.  X  50.  In  the  processes  of  fixing  and 
hardening  the  epithelium  has  become  somewhat  shrunken,  so  that  spaces  occur  between  it  and  the 
interstitial  connective  tissue.  Techn.  No.  141. 

because  they  continually  unite  with  one  another  under  narrow  angles. 
Not  far  from  the  mediastinum  the  convoluted  tubules  pass  into  the  straight 
tubules,  which  considerably  reduced  in  size  (20  to  25  p.  thick),  after  a 


THE  MALE  REPRODUCTIVE  ORGANS. 


29I 


short  course  penetrate  into  the  mediastinum  and  form  the  rete  testis,  the 
tubules  of  which  measure  from  24  to  180  /*  (Fig.  214). 

The  walls  of  the  convoluted  tubules  horn  without  inward  consist  of  (i) 
several  layers  of  flattened  endothelioid  connective-tissue  cells,  (2)  a  thin 
membrana  propria,  and  (3)  of  a  stratified  epithelium,  the  character  of  which 
varies  greatly  in  the  several  divisions  of  the  tubules.  When  the  gland 
is  in  a  state  of  rest  several  strata  of  spherical  cells,  the  nuclei  of  which 
stain  more  or  less  intensely,  may  be  seen  lining  the  tubules  (Fig.  215). 


Spermatids. 

Sertoli's  cells. 
Spermatogenic  cell. 


Blood-vessel  with 
blood-corpuscles. 


Fat- 
globules. 


Spermatids. 


Sertoli's  cells.        Spermatogenic  cells,  above        Sertoli's  cells, 
each  a  large  mother-cell. 


FIG.  216.— CROSS-SECTION  OF  SEMINIFEROUS  TUBULES  OF  A  MOUSE.  X  360.  Observe  that  the  nuclei 
of  the  spermatids  (below  on  the  left)  at  first  round,  become  oval  (above)  and  are  transformed  (below 
on  the  right)  into  the  heads  of  the  seminal  filaments.  Techn.  No.  142. 


In  a  state  of  activity  the  epithelium  exhibits  a  cycle  of  phenomena  relating 
to  spermatogenesis.  The  cells  lying  next  to  the  basement  membrane,  the 
parietal  stratum,  are  of  two  kinds,  the  sustentacular  cells  or  Sertoli  's  col- 
umns, which  take  no  direct  part  in  the  production  of  the  seminal  filaments, 
and  the  Spermatogenic  cells  (ancestral  cells),  the  real  producers  of  the 
semen  (Fig.  216).  They  multiply  by  indirect  division  and  grow  to  be 
large  cells,  that  occupy  the  next  layer  within.  These  are  the  motlicr- 
cclls,  which  divide  twice,  each  giving  rise  to  four  daughter-cells  lying  in 


2Q2  HISTOLOGY. 

a  zone  still  nearer  to  the  center  of  the  tubule.  The  latter  are  the  sper- 
matids  and  from  them  the  spermatozoa  are  directly  derived.  The  nucleus 
of  each  spermatid  develops  into  the  head  of  a  spermatozoon,  a  small 
portion  of  the  protoplasm  forms  the  caudal  filament.  The  middle-piece 
reacts  like  paranuclein  and  probably  is  derived  from  the  centrosome. 
While  these  changes  are  in  progress  the  columns  of  Sertoli  grow  in 
length  centrad  and  a  large  number  of  spermatids  form  a  connection  with 
each  one  of  them  ;  *  it  is  highly  probable  that  by  means  of  this  "  copu- 
lation "  the  spermatids  receive  their  nutritive  material. 

The  walls  of  the  tubuli  recti  consist  of  a  membrana  propria  and 
within  this  of  a  simple  layer  of  low  columnar  cells. 

The  canals  of  the  rete  testis  are  lined  by  a  simple  stratum  of  cubical 
or  flat  epithelial-cells. 

The  arteries  of  the  testicles  are  branches  of  the  spermatic  artery, 
which  proceed  in  part  from  the  mediastinum  and  in  part  from  the  tunica 
vasculosa  to  the  intertubular  septa,  and  there  break  up  into  capillary  net- 
works which  surround  the  seminiferous  tubules.  The  veins  arising  from 
these  networks  follow  the  course  of  the  arteries.  The  lymph-vessels  form 
a  plexus  beneath  the  tunica  albuginea,  which  is  in  connection  with  the 
network  of  lymph-capillaries  enveloping  the  seminiferous  tubules.  The 
nerves  form  networks  about  the  blood-vessels ;  whether  single  fibers 
branch  off  from  these  networks,  pierce  the  membrana  propria,  and 
terminate  in  club-shaped  endings  between  the  epithelial-cells  is  not  yet 
definitely  established. 

THE  SEMEN. 

The  secretion  of  the  testicles,  the  semen,  almost  exclusively  consists 
of  spermatozoa,  pin-shaped  structures  in  which  a  head  and  a  tail  are  dis- 
tinguished (Fig.  217).  In  man  the  head  is  from  3  to  5  /*  long  and  from 
2  to  3  i*  broad,  flattened,  viewed  from  the  side  pyriform  in  shape,  with 
the  tapering  end  directed  forward,  seen  from  surface  oval,  with  the  ante- 
rior end  rounded  and  containing  a  clear  portion  (Fig.  217,  i).  The  tail 
when  very  highly  magnified  exhibits  a  filament  extending  from  end  to 
end,  the  axial  fiber,  which  is  composed  of  delicate  fibrils.  Three  divi- 
sions are  recognized  in  the  tail  :  the  round  middle-piece,  lying  next  to  the 
head,  6  A*  long  and  scarce  I  /*  broad  ;  following  this  the  main-piece,  from 
40  to  60  A*  long,  gradually  diminishing  in  thickness  posteriorly  ;  the  tip 


*  Whence  the  "  spermatoblast  "  of  authors,  see  Techn.  No.  143,  p.  317. 


THE  MALE  REPRODUCTIVE  ORGANS.  2Q3 

of  the  tail,  the  end-piece,  is  about  10  />-  long  and  consists  of  the  project- 
ing axial  fiber.* 

The  spermatozoa  are  distinguished  by  their  extraordinary  vitality 
(probably  due  to  the  calcareous  substances  which  they  contain). 

The  sinuous  movements  of  the  sper- 
matozoa are  executed  by  the  cilium  alone, 
which  propels  the  head  before  it  ;  they 
seldom  occur  in  the  concentrated  secretion 
of  the  testicle  and  first  begin  only  after 
dilution  normally  effected  by  admixture  of 
the  fluids  of  the  ampullae,  of  the  seminal 
vesicles,  of  the  prostate  gland,  and  of  the 
bulbo-urethral  glands.  In  this  mixture  of 
fluids  the  motions  may  continue  for  from 

r  c  .     1   .    i  r.          i       .-i  surface.      2.   Viewed   in  profile.     3. 

tweilty-IOUr  tO  forty  -eight  hours  alter  death  Coiled  seminal  filament.    4.  Sperma- 

.  .  tozoon  of  ox  ;    a,  head  ;    b,  middle- 

for  a  Still  longer  period  111  the  Secretions  piece;  c,  main-piece.    The  end-piece 

t        t  and  the  demarcation  of  these  parts 


t        t 

Of  the    female    genitalia.        Water    paralyzes  cannot  be  perceived  with  this  mag- 

nification.    Techn.  No.  144. 

the    movement,   which,   however,    may  be 

restored  by  the  addition  of  normal  animal  fluids  of  alkaline  reaction  and 
moderate  concentration  ;  normal  fluids  in  general,  also  a  one  per  cent,  salt 
solution,  exert  a  favorable  influence  on  the  vibrations  of  the  spermatozoa, 
while  acids  and  metallic  salts  suspend  them.  In  motionless  spermatozoa 
the  caudal  filament  is  frequently  looped  (Fig.  217,  3). 


THE  EXCRETORY  DUCTS  OF  THE  TESTICLE. 

The  excretory  ducts  of  the  testicle  include  the  epididymis,  the  ductus 
deferens,  the  seminal  vesicles,  and  the  ejaculatory  duct.  (The  tubuli 
recti  and  rete  testis  belong  to  the  excretory  ducts,  but  were  described 
with  the  gland  because  they  are  enclosed  within  it.)  From  the  upper 
end  of  the  rete  testis  about  fifteen  ductuli  efferentes  testis  emerge,  which 
by  their  progressively-increasing  convolutions  form  as  many  conical 
lobules,  the  lobuli  epididymidis.  The  aggregate  of  the  lobuli  constitute 
the  so-called  head  of  the  epididymis.  •  By  the  union  of  the  ductuli  effer- 
entes the  ductus  epididymidis  arises,  which  with  its  complex  convolutions 
forms  the  body  and  tail  of  the  epididymis  and  then  continues  as  the 
ductus  deferens. 

*  The  forms  of  spermatozoa  in  different  animals  cannot  be  described  here.  In  birds  and 
tailed  amphibians  a  spiral  fiber,  united  to  the  axial  fiber  by  a  hyaline  membrane,  has  been  dis- 
covered ;  it  has  also  been  found  in  the  rat  and  other  mammals,  but  has  not  been  demonstrated 
with  certainty  in  man. 


294  HISTOLOGY. 

The  ductuli  efferentcs  are  lined  by  an  epithelium  consisting  of  totally 
dissimilar  varieties  ;  groups  of  simple  ciliated  cylindrical  elements  alter- 
nate with  clusters  of  cubical  cells  without  cilia  ;  consequently  the  latter 
have  the  appearance  of  simple  saccular  glands,  that,  however,  do  not 
produce  evaginations  of  the  membrana  propria  (Fig.  218).  A  fibrous 
membrana  propria  and  a  tunic  of  nonstriped  muscle  consisting  of  several 
circular  strata  complete  the  walls  of  the  ductuli  efferentes.  • 

The  ductus  epididymidis  possesses  a  stratified  ciliated  epithelium  ;  its 
convolutions  are  supported  and  held  together  by  a  loose,  vascular  con- 
nective tissue  ;  toward  the  ductus  deferens  the  circular  strata  of  muscle- 
fibers  increase  in  thickness  (Fig.  218). 

Cubical  cells.  Columnar  cells. 


Smooth  muscle-fibers. 


FIG.  218.—  TRANSVERSE  SECTION  OF  AN  ADULT  HUMAN  DUCTULUS  EFFERENS  TESTIS.  The  right-hand 
end  of  the  illustration  is  schematic.  No  cilia  could  be  seen,  although  those  of  the  epithelium  of  the 
epididymis  were  well  preserved.  Techn.  No.  147. 


The  ductus  deferens  consists  of  either  a  two-layered  columnar 
epithelium  or  of  a  transitional  epithelium,  a  layer  of  connective  tissue 
divided  into  a  tunica  propria  and  a  submucosa,  an  inner  circular  and  an 
outer  longitudinal  stratum  of  smooth  muscle-fibers,  and  a  fibro-elastic 
adventitia.  The  latter,  notably  in  the  division  lying  between  the  testicle 
and  the  ejaculatory  duct,  contains  longitudinally-disposed  bundles  of 
smooth  muscle-fibers  *  (Fig.  219).  In  the  initial  portion  of  the  ductus 
deferens  there  also  is  a  thin  layer  of  longitudinal  nonstriped  muscle- 
fibers  in  the  submucosa.  The  terminal  portion  expands  forming  the 
ampulla,  the  walls  of  which  are  thinner,  but  otherwise  exhibit  a  similar 
structure.  In  the  mucous  membrane  of  the  ampulla  there  are  branched 
gland-follicles  ;  the  columnar  cells  of  the  epithelium  contain  numerous 
pigment-granules.  The  seminal  vesicles  have  the  same  structure.  The 
ejaculatory  duct  consists  of  a  simple  columnar  epithelium  and  thin  inner 


*  They  really  belong  to  the  tunica  vaginalis  of  the  spermatic  cord  (funiculus  spermaticus), 
and  are  known  as  the  musculus  cremaster  internus. 


THE  MALE  REPRODUCTIVE  ORGANS.  2Q5 

circular  and  outer  longitudinal  strata  of  smooth  muscle-fibers,  as  well  as 
an  adventitia  containing  dense  venous  plexuses. 

Excepting  the  networks  around  the  blood-vessels,  the  nerves  form 
an  intricate  plexus  provided  with  sympathetic  ganglia,  the  plexus 
myospcnnaticnSi  situated  in  the  muscularis  of  the  epididymis  and  in  that 


Stratified  ciliated  epithelium. 


—  Membrana  propria. 

—  Circular  muscle-fibers. 
Loose  connective  tissue. 


FIG.  219.— TRANSVERSE  SECTION  OF  A  HUMAN  DUCTUS  EPIDIDYMIDIS.    X  80.    Techn.  No.  147. 

of  the  ductus  deferens,  where  it  is  even  more  dense,  from  which  delicate 
fibers  continue  into  the  mucous  membrane. 

The  paradidymis  (Giraldes),  lying  between  the  convolutions  of 
the  epididymis  and  the  ductulus  aberrans  (Haller)  are  atrophic  remains 
of  the  embryonal  mesonephros.  Both  consist  of  tubules  lined  by 
ciliated  cubical  or  cylindrical  epithelium  and  enveloped  by  a  vascular 


A—  Columnar  epithelium. 
'  i r      Tunica  propria. 
Submucosa. 


Longitudinal  muscle. 


FIG.  220.— TRANSVERSE  SECTION  OF  THE  INITIAL  PORTION  OF  A  HUMAN  DUCTUS  DEFERENS.  X  240. 
The  transversely-cut  longitudinal  muscle-fibers  of  the  submucosa  appear  as  minute  circles  and  dots. 
Techn.  No.  147. 

connective  tissue.  The  appendix  testis  or  hydatid  of  Morgagni  is  a  solid 
lobule  composed  of  a  highly-vascular  connective  tissue  and  covered  by 
a  ciliated  columnar  epithelium  ;  it  possesses  a  short  pedicle,  which  con- 
tains a  duct  lined  by  ciliated  columnar  epithelium.  The  inconstant 
appendix  epididymidis  is  a  vesicle  lined  by  cubical  epithelial-cells  and 


296  HISTOLOGY. 

contains  a  clear  fluid.  The  meaning  of  these  appendices  has  not  yet 
been  fully  explained ;  it  is  uncertain  whether  they  are  remains  of  the 
anterior  end  of  the  embryonal  Miillerian  duct,  that  in  the  female  becomes 
the  fallopian  tube,  or  remnants  of  the  primitive  kidney. 


THE  PROSTATE  BODY. 

The  prostate  body  consists  for  the  lesser  part  of  glandular  tissue, 
for  the  greater  part  of  nonstriped  muscle-fibers.  The  glandular  portion 
is  composed  of  from  thirty  to  fifty  simple  branched  tubular  serous 
glands,  which  are  characterized  by  their  loose  structure,  that  is,  by  the 
wide  intervals  between  the  tubules.  The  tubules  open  by  two  large  and 
a  number  of  smaller  ducts  into  the  urethra.  The  glandular  cells  are  low 
columnar  elements,  which  in  a  simple  layer  line  the  tubules.  In  the 
larger  ducts  the  epithelium  is  of  the  transitional  variety,  like  that  in  the 
prostatic  portion  of  the  urethra.  In  elderly  persons  the  so-called  prostatic 
crystals — round  stratified  masses  of  secretion  up  to  0.7  mm.  in  size — 
occur  in  the  gland-tubules.  The  involuntary  muscle-fibers,  found  in 
large  quantities  everywhere  between  the  gland-lobules,  are  augmented 
toward  the  urethra  and  form  a  robust  circular  layer  (the  internal  vesical 
sphincter  muscle) ;  numerous  involuntary  muscle-fibers  are  also  found 
on  the  external  surface  of  the  prostate  body,  where  they  are  contiguous 
to  the  bundles  of  striated  muscle-fibers  of  the  musculus  sphincter 
urethrae  membranaceae.*  The  prostate  gland  and  the  colliculus  seminalis 
are  provided  with  many  blood-vessels.  Regarding  the  terminations  of 
the  numerous  nerves  nothing  is  definitely  known. 

The  glandules  bulbo-urethrales  (Cowper)  are  compound  tubular 
glands,  the  wide  tubules  of  which  are  clothed  with  a  simple  layer  of 
clear  columnar  cells,  the  excretory  duct  of  which  is  lined  with  two  or 
three  strata  of  cubical  cells. 

THE  PENIS. 

The  penis  consists  of  three  cylindrical  bodies  :  the  two  corpora 
cavernosa  and  the  corpus  spongiosum,  which  are  enveloped  by  fascia  and 
skin. 

Each  corpus  cavernosum  is  composed  of  a  fibrous  sheath,  the 
tunica  albuginea,  and  of  erectile  tissue.  The  tunica  albuginca  is  a  stout 
connective-tissue  membrane,  possessing  an  average  thickness  of  I  mm., 

*  Both  sphincters  are  now  designated  musculus  prostaticus. 


THE  MALE  REPRODUCTIVE  ORGANS. 


297 


intermingled   with  many   elastic  fibers,  in   which   an  outer  longitudinal 
and  an  inner  circular  layer  may  be  distinguished. 

The  erectile  tissue  is  established  by  lamellae  and  trabeculae  of 
connective  tissue  containing  bundles  of  smooth  muscle-fibers,  that  by 
means  of  numerous  anastomoses  form  a  network  the  spaces  of  which 
are  lined  by  a  single  stratum  of  flat  epithelial-cells.  The  spaces  are 
filled  with  venous  blood.  The  thick-walled  arteries  in  part  pass  into 
capillaries,  in  part  open  directly  into  the  deep  cortical  plexus.  The 
capillaries  form  a  network  beneath  the  tunica  albuginea,  the  superficial 
(fine)  cortical  plexus,  which  is  connected  with  a  many-layered  net  of 
wider  venous  channels,  the  deep  (coarse)  cortical  plexus.  The  latter  lies 


Epithelium. 


Mucosa. 


Submucosa. 


«  3C 


48S- 


J^-   ,  Cavernous  tissue. 


ica  albuginea. 


FIG.  221.— FROM  A  TRANSVERSE  SECTION  OF  THE  CAVERNOUS  PORTION  OF  THE  HUMAN  URETHRA. 
X  20.  /,  Urethral  glands ;  the  lowermost  line  indicates  the  fundus  of  the  gland,  the  upper  lines,  por- 
tions of  the  excretory  duct;  g,  blood-vessels;  m,  transverse  section  of  longitudinally-disposed 
muscle-fibers  ;  r,  superficial  cortical  capillary  network.  Techn.  No.  148. 


in  the  superficial  strata  of  the  erectile  tissue  and  gradually  passes  into 
the  venous  spaces  of  the  same.  The  so-called  lielicine  arteries  are  small 
branches  lying  within  slender  connective-tissue  cords,  which  protrude  as 
loops  in  the  cavernous  spaces  and  in  an  imperfect  injection  appear  to 
terminate  in  blind  ends.  The  veins  which  return  the  blood  from  the 
corpora  cavernosa  partly  arise  from  the  deep  cortical  plexus,  partly  from 
the  deeper  portions  of  the  erectile  tissue.  They  penetrate  the  tunica 
albuginea  and  empty  into  the  dorsal  vein  of  the  penis. 

The  corpus  spongiosuin  consists  of  two  different  divisions  ;  the  cen- 
tral portion  is  formed  by  a  reticulum  of  the  conspicuously-developed 
veins  of  the  submucosa  of  the  urethra  ;  the  peripheral  portion  resembles 


298  HISTOLOGY. 

in  structure  the  corpora  cavernosa,  excepting  that  there  is  no  direct 
communication  of  the  arteries  with  the  venous  spaces.  The  tunica 
albuginea  is  composed  of  a  layer  of  circularly-arranged  bundles  of 
fibrous  tissue.  The  glans  consists  of  greatly-convoluted  veins,  that  are 
held  together  by  a  well-developed  connective  tissue,  the  carrier  of  the 
arterioles,  and  by  the  capillaries. 


THE    FEMALE    REPRODUCTIVE    ORGANS. 

THE  OVARIES. 

The  ovaries  consist  of  connective  tissue  and  glandular  substance. 
The  compact  connective  tissue,  the  ovarian  stroma,  is  arranged  in  several 
strata ;  outermost  lies  the  tunica  albuginea,  a  structure  composed  of 
two  or  more  intersecting  lamellae  of  connective  tissue,  which  pass  by 
imperceptible  gradations  into  the  stroma  of  the  cortex ;  the  latter 
encloses  the  glandular  substance  and  is  continuous  with  the  medulla, 


FIG.  222. — TRANSVERSE  SECTION  OF  THE  OVARY  OF  A  CHILD  EIGHT  YEARS  OLD.  X  10.  i.  Germinal 
epithelium  ;  2,  tunica  albuginea,  as  yet  but  slightly  developed  ;  3,  outermost  zone  of  the  cortex  con- 
taining numerous  minute  follicles;  4,  larger  follicle;  5,  inner  division  of  cortex  ;  6,  medulla  with 
numerous  tortuous  arteries;  7,  follicle  cut  at  the  periphery;  8,  large  follicle,  the  cumulus  ovigerus 
not  within  the  plane  of  the  section  ;  9,  hilus,  containing  wide  veins.  Techn.  No.  149. 

which  contains  numerous  convoluted  blood-vessels  and  strands  of 
smooth  muscle-fibers  accompanying  them.  The  glandular  substance  is 
formed  by  a  profusion  of  spherical  epithelial  sacs,  the  egg -follicles, 
each  of  which  contains  an  ovum.  In  the  human  ovary  there  are 
about  36,000  follicles.  The  majority  of  the  follicles  are  microscopic 
in  size  (40  /*)  and  in  the  outermost  stratum  of  the  cortex  form  an  arched 
zone  embracing  the  entire  organ  except  at  the  hilus,  where  the  vessels 


THE  FEMALE  REPRODUCTIVE  ORGANS. 


299 


Germinal  epithelium. 
Egg-ball. 


Primordial  ovum. 


Germinal  spot. 
Germinal  vesicle. 
Vitellus. 

Follicular 
epithelium. 

FIG.  223. — FROM  A  VERTICAL  SECTION  OF  AN  OVARY  OF  AN 
INFANT  FOUR  WEEKS  OLD.  X  240.  The  primordial  ovum  has  a 
large  nucleus  with  a  nucleolus.  The  egg-ball  contains  three 
ova,  surrounded  by  cylindrical  cells.  Techn.  No.  149. 


and  nerves  enter.  The  larger  follicles  occupy  the  deeper  portions  of 
the  cortex.  The  largest,  those  follicles  readily  perceptible  by  the 
unaided  eye,  when  fully  developed  extend  from  the  medulla  to  the  tunica 
albuginea.  The  surface  of  the  ovary  is  covered  by  a  simple  layer  of 
very  small,  mostly  short  cylindrical  cells,  the  germinal  epithelium. 

Only  the  initial  stage  in  the  development  of  the  ova  takes  place 
during  the  embryonal 
period  ;  their  subsequent 
development,  from  the 
primordial  to  the  fully- 
ripened  follicle,  may  be 
observed  in  all  its  phases 
in  every  functionally  ac- 
tive ovary.  During  the 
fetal  period  many  cells  of 
the  germinal  epithelium 

divide  into  two  cells  lying  one  above  the  other,  of  which  the  lower 
enlarges  and  becomes  the  primordial  ovum  with  its  conspicuous  nucleus 
and  nucleolus,  while  the  upper  cell  and  also  its  neighbor-cells  become 
flattened  and  apply  themselves  scale-like  around  the  ovum.  Such  con- 
ditions are  still  found  after  birth  (Fig.  223).  The  ovum,  which  under 
circumstances  may  divide  once  more,  surrounded  by  its  indifferent 

neighbor-cells,  moves  down 
into  the  ovarian  stroma,  while 
above  in  the  germinal  epithe- 
lium new  primordial  ova  arise 
in  the  same  way,  that  likewise 
move  into  the  depths.  Thus 
originate  entire  complexes  of 
egg-cells  and  indifferent  cells 
of  the  germinal  epithelium, 
\v  which  are  named  egg-balls 
Theca  foiiicuii.  (  egg  -  pouches,  egg  -  nests  ). 

Each  ovum  subsequently  be- 
comes separated  '  from  its 
neighbor  by  the  rapid  multiplication  of  the  indifferent  epithelial-cells, 
as  well  as  by  proliferation  of  the  connective  tissue,  and  is  then  an 
isolated,  spherical  body,  the  primitive  follicle,  that  consists  of  the  ovum 
and  the  epithelial-cells  enclosing  it,  the  so-called  follicular  epithelium,  and 
of  a  connective-tissue  sheath.  So  far  the  processes  are  chiefly  fetal. 
The  cells  of  the  follicular  epithelium  now  grow  taller  (Fig.  224),  then 


Germinal  epithelium. 

Tunica  albuginea. 

Primitive  follicle. 


Follicle  with  a  simple  stratum 
of  cylindrical  epithelium. 

Follicular  epithelium. 


Ovum. 


Zona  pellucida. 

Vitellus. 
Germinal  vesicle 

with    germinal 

spot. 


FIG.  224.— FROM  A  SECTION  OF  THE  CORTEX  OF  THE 
OVARY  OF  A  RABBIT.    X  90.    Techn.  No.  149. 


300 


HISTOLOGY. 


become  stratified,  the  ovum  grows  larger,  takes  up  an  eccentric  position 
within  the  follicle,  and  acquires  a  delicate,  radially-striated  border-mem- 
brane that  gradually  increases  in  thickness,  the  sona  pcllucida  (06 lemma). 
With  the  enlargement  of  the  ovum  a  differentiation  of  its  protoplasm  is 
also  completed  ;  the  greater  portion  of  it  is  transformed  into  a  crummy 
mass,  the  deutoplasm ;  of  the  original  protoplasm,  the  egg-protoplasm, 
there  remains  only  a  zone  around  the  eccentrically-situated  nucleus  and 
a  thin  stratum  covering  the  surface  of  the  ovum.  The  deutoplasm  and 
egg-protoplasm  are  together  named  vitcllus ;  the  nucleus  is  called  germinal 
vesicle  (vesicula  germinativa),  which  contains  the  germinal  spot*  (macula 
germinativa).  Ameboid  movements  have  been  observed  in  the  latter. 


'^s    f  Tunica  externa. 
Tunica    interna. 


Stratum  granulosum. 
(Follicular  epithelium.) 


Cumulus  ovigerus. 


Ovum  with  zona  pellucida, 

germinal  vesicle,  and  germinal 

spot. 


FIG.  225.— SECTION  OF  A  LARGE  GRAAFIAN  FOLLICLE  OF  A  CHILD  EIGHT  YEARS  OLD.    X  90.    The  clear 
space  within  the  follicle  contains  the  liquor  folliculi.    Techn.  No.  149. 

The  follicle  now  develops  further  ;  during  continual  multiplication  of 
the  cells  of  the  follicular  epithelium  a  cleft  appears  in  their  midst  that  be- 
comes filled  with  a  fluid  substance,  the  liquor  folliculi.  This  liquid  is  partly 
a  transudate  from  the  blood-vessels  surrounding  the  follicle,  partly  derived 
from  the  liquefaction  of  some  of  the  cells  of  the  follicular  epithelium  ;  it 
progressively  increases  in  quantity  and  the  follicle  expands  to  a  vesicle, 
the  Graafian  follicle  (folliculus  Vesiculosus),  having  a  diameter  of  from 


*  The  germinal  spot  cannot  be  regarded  as  a  nucleolus,  since  it  differs  from  this  in  its 
chemical  relations.     It  is  not  composed  of  paranuclein,  but  of  a  substance  resembling  nuclein. 


THE  FEMALE  REPRODUCTIVE  ORGANS. 


301 


o.  5  to  12  mm.  Around  the  larger  follicles  the  connective  tissue  of  the 
stroma  is  arranged  in  circular  strands  forming  a  sheath  called  the  theca 
folliculi  (Fig.  224),  in  which  an  outer  fibrous  layer,  the  tunica  externa, 
and  an  inner  vascular  layer  rich  in  cells,  the  tunica  interna,  may  be  distin- 
guished (Fig.  225).  The  stratified  follicular  epithelium,  which  in  teasing 
fresh  follicles  becomes  detached  in  large  shreds,  has  long  been  known  as 
the  stratum  (mtmbrana)  granulosum  ;  at  one  point  it  presents  a  thicken- 
ing, the  discus  proligerus  or  cumulus  ovigerus,  which  encloses  the  ovum. 
The  cells  of  the  cumulus  which  lie  next  to  the  zona  pellucida  are  radially 
placed  to  the  ovum  and  form  the  corona  radiata  (Fig.  226).  The 


Zona  pellucida. 
Vitellds. 


Zona  pellucida.  — 
Vitellus.  — ? 

Cells  of  the  cu- 
mulus ovigerus. 


Germinal 
vesicle. 


Germinal  spot. 


Corona  radiata 

(cells  of  the 

cumulus). 


FIG.  226. — AN  OVUM  FROM  THE  GRAAFIAN  FOLLICLE  OF  A  Cow.    A  magnified  50,  B  magnified  240  times, 
The  radial  striation  of  the  zona  pellucida  cannot  be  seen.    Techn.  No.  150. 


greater  part  of  the  interior  space  of  the  follicle  is  occupied  by  the  liquor 
folliculi. 

When  the  vesicular  follicle  has  attained  its  full  development,  it 
bursts  at  the  pole  directed  toward  the  surface  of  the  ovary,  where  its 
site  is  previously  indicated  by  the  attenuated  and  arched  overlying  tissue  ; 
the  ovum  enveloped  by  the  cumulus  escapes  into  the  pelvic  cavity,  the 
empty  follicle  undergoes  regressive  change  and  is  converted  into  the 
yellow  body,  the  corpus  lutcum.  When  the  discharged  ovum  is  not 
fertilized  the  yellow  body  disappears  after  the  lapse  of  a  few  weeks  ;  it  is 
then  called  the  false  corpus  luteum  ;  if  on  the  other  hand  the  escape  of 
the  ovum  is  followed  by  pregnancy,  the  ruptured  follicle  develops  into 
the  true  yelloiv  body,  which  possesses  a  diameter  of  about  one  centimeter 
and  endures  for  years.  It  consists  of  a  fibrous  membrane  (the  former 
tunica  externa)  and  of  a  yellow  mass  that  has  arisen  by  the  enlargement 
of  the  fatty,  metamorphosed  cells  of  the  follicular  epithelium  and  by 


302 


HISTOLOGY. 


proliferation  of  the  cells  of  the  tunica  interna  ;  the  latter  are  transformed 
into  delicate  connective-tissue  septa,  that  penetrate  between  the  cells  of 
the  follicular  epithelium  (Fig.  227).  In  the  center  of  the  corpus  luteum 
there  occasionally  is  a  cavity  filled  with  blood.  The  blood  is  derived 
from  the  torn  vessels  of  the  tunica  interna.  Later  the  center  becomes 
decolorized  and  the  blood-clot  is  replaced  by  a  crummy  mass  occasionally 
containing  hematoidin  crystals  (see  p.  121). 

Not  all  the  primitive  follicles  attain  complete  development.  Many 
undergo  regressive  change.  Retrograde  metamorphosis  of  mature 
follicles  also  occurs.  This  process  is  effected  as  follows  :  first  the  ovum 
dies  and  then  cells,  in  part  elements  of  the  stratum  granulosum,  in  part 


Connective-tissue  septa. 


Fibrous  membrane. 


^^gy 

~y$? 

®     M,        v-y Oil  droplets. 


FIG.  227.— A.  Portion  of  a  corpus  luteum  of  a  rabbit.  B.  Portion  of  a  corpus  luteum  of  a  cat.  X  260. 
In  B  the  foliicular  epithelium  is  undergoing  fatty  degeneration  and  the  cells  are  filled  with  oil- 
droplets. 

leucocytes,  wander  into  the  ovum  and  liquefy  and  absorb  its  substance. 
Having  completed  the  disintegration  and  resorption  of  the  vitellus,  the 
migrated  cells  perish. 

The  arteries  of  the  ovary,  branches  of  the  ovarian  and  the  uterine 
arteries,  enter  at  the  hilus,  divide  in  the  medulla,  and  are  characterized  by 
their  tortuous  course  (Fig.  222).  From  the  medulla  they  pass  to  the 
cortex,  where  they  chiefly  supply  capillary  networks  situated  in  the 
tunica  interna  of  the  follicles.  The  veins  form  a  dense  plexus  at  the 
hilus  of  the  ovary.  The  lymph-vessels  are  numerous  and  may  be  traced 
to  the  tunica  interna  of  the  follicles.  Medullated  and  nonmedullated 
nerves  in  large  number  enter  at  the  hilus  in  company  with  the  blood- 
vessels, to  the  walls  of  which  the  majority  of  them  are  distributed.  A 


THE  FEMALE  REPRODUCTIVE  ORGANS.  303 

few  of  the  nerves  proceed  to  the  cortex  ;  these  form  there  a  dense  plexus 
of  delicate,  mostly  gray  fibers,  which  embraces  the  follicle  and  sends 
minute  fibrils  to  the  walls  of  the  blood-vessels  ;  whether  nerve-fibers 
penetrate  within  the  epithelium  of  the  larger  follicles  is  not  yet  definitely 
established. 

The  epoophoron  and  the  paroophoron  are  remains  of  embryonal 
structures.  The  former  lies  within  the  lateral  portion  of  the  broad  liga- 
ment (mesosalpinx)  at  the  hilus  ovarii  (in  the  cat,  mouse,  etc.,  within  the 
hilus)  and  consists  of  a  group  of  convoluted  blind  tubules,  the  walls  of 
which  consist  of  ciliated  columnar  epithelium  and  circularly-arranged 
connective-tissue  fibers.  The  epoophoron  is  the  remains  of  the  middle 
or  sexual  segment  of  the  primitive  kidney.  The  paroophoron  lies  in  the 
median  division  of  the  mesosalpinx  and  consists  of  branched  tubules  lined 
with  ciliated  columnar  epithelium  ;  it  represents  the  posterior  segment  of 
the  mesonephros. 

THE  OVIDUCT. 

The  walls  of  the  oviduct  or  fallopian  tube  consist  of  three  coats  :  an 
inner  mucous,  a  middle  muscular,  and  an  outer  serous.  The  mucous  mem- 
brane is  thrown  into  numerous  longitudinal  folds,  so  that  on  transverse 
section  the  lumen  of  the  narrow  portions  of  the  oviduct  has  a  stellate  out- 
line. The  folds  correspond  in  amplitude  to  the  size  of  the  tube  and  are 
highest  in  the  ampulla,  where  they  are  united  to  one  another  by  minute 
oblique  secondary  plications.  The  thick  mucous  coat  is  composed  of  (i) 
a  fibro-elastic  tunica  propria  containing  numerous  connective-tissue  cells, 
(2)  of  a  layer  of  simple  ciliated  columnar  epithelium,  the  ciliary  wave  is 
directed  toward  the  uterus,  (3)  of  an  extremely  thin  muscularis  mucosae 
consisting  of  longitudinally-disposed  bundles  of  smooth  muscle-fibers,  and 
(4)  of  a  submucosa  formed  by  a  thin  layer  of  fibrillar  connective-tissue. 
The  muscular  coat  consists  of  an  inner  thicker  circular  and  an  outer  very 
thin  longitudinal  layer  of  involuntary  muscle-fibers.  The  serous  tunic  is 
formed  by  the  peritoneum  and  by  a  considerable  layer  of  loosely-united 
connective-tissue  bundles. 

The  blood-vessels  are  especially  abundant  in  the  mucosa,  where  they 
form  a  narrow-meshed  capillary  network.  The  larger  veins  run  along 
the  base  of  the  longitudinal  folds  of  the  mucosa.  The  knowledge  of  the 
exact  behavior  of  the  lymph-vessels  is  still  wanting.  The  nerves  form  a 
rich  plexus  in  the  mucosa,  from  which  branches  ascend  to  the  epithelium. 
A  penetration  in  the  epithelium  has  not  been  observed. 


304 


HISTOLOGY. 


THE  UTERUS.* 

The  walls  of  the  uterus,  like  those  of  the  oviduct,  consist  of  a 
mucosa,  a  muscularis,  and  a  serosa. 

The  serosa  exhibits  no  special  characteristics. 

The  muscularis  consists  of  smooth  muscle-fibers,  united  into  bundles 
which  interlace  in  all  directions,  so  that  a  sharp  demarcation  of  single 
layers  is  not  possible ;  still  in  general  three  strata,  more  or  less  well- 
defined,  maybe  distinguished  :  (i)  an  inner  layer  (stratum  submucosum), 
chiefly  composed  of  bundles  disposed  in  a  longitudinal  direction  ;  (2)  a 
middle  layer,  the  most  robust,  consisting  of  bundles  having  in  general  a 


Mucosa. 


Muscularis 


is.  {3    ( 


Serosa.       

FIG.  228. — FROM  A  TRANSVERSE  SECTION  OF  THE  MIDDLE  OF  THE  UTERUS  OF  A  GIRL  FIFTEEN  YEARS 
OLD.  X  10.  a,  Epithelium;  d,  tunica  propria ;  c,  glands;  i,  inner  muscular  layer  (stratum  submu- 
cosum); 2,  middle  muscular  layer  (stratum  vasculare) ;  3,  outer  muscular  layer  (stratum  supravas- 
cularej.  Techn.  No.  153. 

circular  disposition  and  containing  the  principal  ramifications  of  the 
arteries,  also  a  well-developed  venous  plexus,  hence  the  name  stratum 
vasculare  ;  (3)  an  outer  layer  (stratum  supravasculare),  formed  of  bundles 
extending  partly  in  a  circular,  partly  in  a  longitudinal  direction,  the 
latter  close  beneath  the  serosa,  with  which  they  are  intimately  united. 
The  stratification  of  the  muscular  tissue  is  more  pronounced  in  the  cervix, 
where  an  inner  and  an  outer  longitudinal  may  be  distinguished  from  a 
middle  circular  layer.  The  volume  of  the  muscularis  is  subject  to  great 
variation,  dependent  on  the  functional  state  of  the  uterus. 

*  This  chapter  has  been  revised  and  considerably  enlarged  by  the  editor. 


THE  FEMALE  REPRODUCTIVE  ORGANS. 


305 


The  muscle-fibers  differ  somewhat  from  the  elements  of  smooth 
muscle-tissue  as  found  in  other  organs.  They  are  elongated  cells, 
usually  spindle-shaped,  or  are  blunted  and  frayed  at  the  ends.  Fre- 
quently they  are  forked  at  their  extremities.  Their  length  varies  greatly, 
in  the  virgin  uterus  from  40  to  60  // ;  during  pregnancy  they  increase 
excessively  and  at  the  end  of  the  same  attain  a  size  of  from  300  to  600  /*. 
The  nucleus  (not  infrequently  two  or  more  are  present  in  one  cell)  is  usually 
oval  and  lies  embedded  in  a  granular  substance. 

The  mucosa  is  sharply  defined  from  the  muscularis.  It  is  the  coat 
which  in  the  different  functional  states  of  the  uterus  undergoes  the  pro- 


•'!    '• 


Epithelium. 

'W 


—  Gland-tubule. 


>•-    Mucosa. 


FIG.  229. — Mucous  MEMBRANE  OF  THE  RESTING  UTERUS  OF  A  YOUNG  WOMAN.    X  35- 
{After  Bohm  and  von  Davidoff.} 

foundest  and  physiologically  the  most  important  changes.     A  description 
of  the   histologic  structure  of  the  mucosa  of  the  uterus  can,  therefore, 
only  answer  to  the  corresponding  functional  condition  of  the  organ,  and 
in  consideration  hereof  will  be  presented  in  separate  sections. 
It  is  desirable  to  consider  : — 

1.  The  mucosa  of  the  virgin  resting  organ. 

2.  The  mucosa  of  the  menstruating  uterus. 

3.  The  mucosa  of  the  gravid  uterus. 

The  mucosa  of  the  virgin  resting  uterus  (Fig.  229),  after  the  advent 


306  HISTOLOGY. 

of  puberty,  has  a  thickness  of  from  I  to  2  mm.  and  bears  on  its  surface 
a  single  layer  of  ciliated  columnar  epithelium,  30  p.  in  height  in  the  middle 
regions  ;  the  ciliary  wave  is  directed  toward  the  cervix.  The  tunica 
propria  is  formed  of  a  fine  fibrous  tissue  closely  resembling  embryonal 
connective  tissue  ;  it  consists  of  elongated  cells  furnished  with  oval  nuclei, 
which  send  out  in  all  directions  branched  processes  that  unite  with  those 
of  neighboring  cells  and  so  form  a  cellular  network,  the  meshes  of  which 
are  occupied  by  lymph  and  numerous  leucocytes. 

The  tunica  propria  supports  many  simple  or  forked  gland-tubules,  of 
which  the  upper  part  pursues  a  course  more  or  less  vertical  to  the  surface 
of  the  mucosa,  while  the  lower  half  usually  appears  irregularly  spiral. 
The  glands  extend  close  up  to  the  muscularis  and  here  not  infrequently 
they  are  bent  at  right  angles,  so  that  the  fundus  runs  parallel  to  the 
muscular  coat.  The  glands  of  the  uterus  are  to  be  regarded  as  imagi- 
nations of  the  superficial  epithelium  and  likewise  consist  of  a  simple  layer 
of  ciliated  epithelium  resting  upon  a  delicate  basement  membrane  com- 
posed of  anastomosing  connective-tissue  cells. 

The  blood-vessels  run  in  a  winding  manner  from  the  muscularis  to 
the  surface  of  the  mucosa  and  the  arteries  in  particular  are  character- 
ized by  their  extremely-convoluted,  corkscrew-like  course.  At  the  sur- 
face they  break  up  into  capillaries  and  form  a  close  network.  A  similar 
network  surrounds  the  gland-tubules.  The  veins  proceeding  from  the 
capillaries  form  a  plexus  in  the  deeper  strata  of  the  mucosa,  that  is  espe- 
cially well  developed  in  the  cervix  and  particularly  around  the  external 
orifice. 

In  the  cervix  the  mucous  membrane  is  thicker  and  in  its  upper  two- 
thirds  is  clothed  with  a  single  layer  of  tall  ciliated  cells  (60  /-/-  high  in  the 
middle  portion),*  while  toward  the  external  orifice  papillae  covered  by  a 
stratified  squamous  epithelium  appear.  In  addition  to  a  few  scattered 
tubular  glands,  mucous  follicles,  the  so-called  mucous  crypts,  occur ;  they 
are  I  mm.  wide,  possess  many  evaginations,  and  by  retention  of  their 
secretion  are  converted  into  cysts,  the  ovula  Nabothi. 

During  the  period  of  menstruation  a  number  of  progressive  and 
regressive  changes  take  place  in  the  mucosa  of  the  uterus,  which  may 
be  grouped  in  three  phases  : — 

(a)  Thickening  of  the  mucosa,  accompanied  by  changes  in  its 
histologic  structure. 

(^)  Menstruation  proper. 

(c)  Regeneration. 


Transformation  of  these  cells  into  goblet-cells  occurs. 


THE  FEMALE  REPRODUCTIVE  ORGANS. 


307 


The  initial  phase  is  characterized  by  a  considerable  increase  in  the 
thickness  of  the  mucosa  (up  to  6  mm.),  in  consequence  of  which  the 
surface  becomes  irregular  and  the  orifices  of  the  glands  open  in  deep 
depressions.  The  thickening  of  the  mucosa  depends  in  a  measure  on 
an  actual  increase  of  the  tissue  produced  by  proliferation  of  the  con- 
nective-tissue cells  and  leucocytes  and  by  growth  of  the  gland-tubules, 


Superficial  epithelium. 


Excretory  duct.   — ; 


—    Excretory  duct. 


-    Muscujaris. 


FIG.  230.— Mucous  MEMBRANK  OF  A  VIRGIN  UTERUS  DURING  THE  FIRST  DAY  OF  MENSTRUATION. 
ds,  Disintegrating  surface;  pd,  pit-like  depression  of  the  mucous  membrane;  gl,  glandular  lumen 
very  much  enlarged.  X  y>.—  (Schaper.} 

which  in  the  process  take  up  an  irregular  course  and  become  essentially 
wider.  Simultaneously  the  blood-vessels,  especially  the  veins  and  capil- 
laries, undergo  enormous  distention,  whereby  the  blood-supply  of  the 
organ  is  extraordinarily  augmented.  In  this  condition  the  mucosa  is 
designated  decidua  incnstrualis. 

These  changes  are  followed  by  a  partial  disintegration  of  the  super- 


308 


HISTOLOGY. 


ficial  strata  of  the  mucosa,  accompanied  by  an  infiltration  of  blood  into 
the  subepithelial  tissues.  The  molecular  disintegration  (associated  with 
fatty  degeneration)  of  the  surface  advances  rapidly,  the  greatly-dilated 
superficial  blood-vessels  become  exposed,  rupture,  and  cause  hemor- 
rhages within  the  uterine  cavity,  which  flow  into  the  vagina  and  give  rise 
to  the  external  phenomena  of  menstmation.  After  this  discharge  of 
blood  the  mucosa  is  rapidly  reduced  in  thickness.  The  surface  is  now 
entirely  devoid  of  epithelium  and  consists  of  connective  tissue  and 
exposed  blood-vessels.  This  condition  is  immediately  succeeded  by  the 


Compact  layer. 


Cavernous  layer. 


Excretorv  duct. 


•H0V- 


Spiral  artery. 


Gland-tubules. 


Musctilaris. 


FIG.  231.— VERTICAL  SECTION  THROUGH  THE  Mucous  MEMBRANE  OF  A  HUMAN  UTERUS  ONE  MONTH 
PREGNANT;  it  shows  the  outlines  of  the  glands  and  the  division  of  the  mucosa  into  an  upper  com- 
pact and  a  lower  cavernous  layer. — (After  Minot.) 


stage 


of  regeneration.  The  hyperemia  rapidly  disappears,  the  extrava- 
sated  blood  is  partly  resorbed,  partly  cast  off,  a  cellular  network  grows 
upward  and  restores  the  lost  tunica  propria,  while  from  the  gland-cells 
the  epithelial  covering  of  the  mucosa  is  regenerated.  New  subepithelial 
capillaries  are  formed. 

The  histology  of  the  mucosa  of  the  uterus  during  pregnancy 
(decidua  graviditatis)  (Fig.  231  and  Fig.  232)  is,  on  the  whole,  like  that 
of  the  decidua  menstrualis,  with  the  alterations  more  pronounced.  It, 
however,  undergoes  considerable  modification  because  of  its  intimate 
relations  with  the  developing  ovum  in  the  uterus.  These  relations  vary, 


THE    FEMALE    REPRODUCTIVE    ORGANS. 


309 


and  thus  in  the  course  of  development  three  essentially  different  parts  of 
the  mucosa  may  be  distinguished  : — 

(<?)  The  dccidua  scrotina  (decidua  basalis),  the  area  of  the  mucosa 
to  which  the  ovum  is  attached  (placenta  uterina). 

(/;)  The  dccidua  vera,  which  comprises  all  the  remaining  portion  of 
the  mucosa  attached  to  the  wall  of  the  uterus. 

(c)  The  dccidua  rcflexa  (decidua  capsularis),  the  portion  of  the 
mucosa  which  projects  into  the  cavity  of  the  uterus  and  encapsules  the 
ovum. 

The  decidua  serotina  and  decidua  vera  undergo  progressive  develop- 


Atiinioii. 


Vein. 


Cavernous  layer. 


—  Gland. 


—  Vein. 


Muscular  is. 


FIG.  232. — VERTICAL  SECTION  THROUGH  THE  WALL  OF  A  UTERUS  ABOUT  SEVEN  MONTHS  PREGNANT, 
WITH  THE  FETAL  MEMBRANES  IN  SITU.  Between  amnion  and  chorion  are  threads  of  the  inter- 
mediate gelatinous  connective  tissue.  X  3°. — (Schaper.) 


ment  during  the  entire  course  of  pregnancy  and  persist  until  its  close  ; 
the  decidua  reflexa  becomes  gradually  attenuated  and  disappears  in  the 
course  of  the  fifth  month. 

A  section  of  the  greatly-thickened  mucosa  (decidua  vera  and 
decidua  serotina)  shows  the  same  histologic  details  that  have  been 
described  in  the  menstrual  decidua,  but  with  this  difference,  that  the 
progressive  alterations  (proliferation  of  the  connective-tissue  elements, 
distention  of  the  blood-vessels  and  glands)  attain  much  greater  proper- 


HISTOLOGY. 


tions.  A  superficial  compact  zone  and  a  deep  spongy  zone  can  always  be 
distinguished  (Fig.  231).  The  cavities  in  the  latter  are  produced  by  the 
lower  divisions  of  the  gland-tubules,  which  have  become  greatly  widened 
and  very  tortuous.  At  a  later  stage  of  pregnancy,  owing  to  the  great 
distention  of  the  uterus,  the  lumina  of  the  glands  appear  compressed 
and  straighter  (parallel  to  the  muscular  coat).  (Fig.  232.)  Between 
the  glands  are  numerous  blood-vessels,  spindle-cells,  and  multinucleated 
giant-cells.  The  epithelium  of  the  glands  early  begins  to  loosen,  and  in 
great  part  the  cells  lie  irregularly  scattered  in  the  lumen  of  the  tubule, 
where  they  disintegrate.  The  orifices  of  the  glands  are  gradually 
obliterated,  since  the  walls  after  the  loss  of  the  epithelium  become 
adherent  and  grow  together. 

The  blood-vessels  of  the  mucosa  are  all  dilated,  especially  the  super- 
ficial veins  and  capillaries  ;  the  latter  often  form  distended  sinus-like 
cavities  in  the  upper  layer  of  the  decidua.  In  the  decidua  serotina  the 
arteries  and  veins  open  on  the  surface  of  the  mucosa  (Fig.  234  and  Fig. 
235),  so  that  here  the  maternal  blood  circulates  between  the  chorionic 
villi  of  the  placenta  (see  page  316).  In  the  decidua  vera  the  blood- 
vessels, toward  the  end 'of  pregnancy,  are  less  conspicuous. 

Of  especial  interest  are  peculiar,  typical  cells,  decidual  cells,  that 
appear  in  large  numbers  in  the  mucosa  of  the  gravid  uterus.  They  are 

flattened,  spherical,  oval,  or  branched  cells 
of  conspicuous  size  (0.03  too. I  mm.),  that 
in  the  latter  half  of  pregnancy  assume  a 
characteristic  brown  color.  They  usually 
possess  but  one  nucleus,  though  occasion- 
ally two,  three,  or  more  are  present,  and  in 
rare  cases  as  many  as  thirty  or  forty.  The 
decidual  cells  are  most  numerous  and  most 
densely  aggregated  in  the  upper  compact 
zone  of  the  serotina  (Fig.  232),  which  owes 
its  typical  character  and  brown  color  to 
these  elements.  Occasionally  cells  are 
found  that  are  united  with  one  another 
by  means  of  protoplasmic  processes. 
According  to  Minot,  the  decidual  cells 
originate  from  connective-tissue  elements, 
therefore  may  be  regarded  as  a  modified 
embryonal  or  so-called  anastomosing  connective  tissue. 

In  a  cross-section  of  the  decidua  vera  in  the  latter  half  of  preg- 
nancy, it  will  be  seen  that  the  surface  of  the  mucosa  is  covered  by  two 


FIG.  233. —  DECIDUAL  CELLS  FROM 
THE  Mucous  MEMBRANE  OF  A  HU- 
MAN UTERUS  ABOUT  SEVEN  MONTHS 
PREGNANT.  Below  a  "giant-cell," 
above  to  the  right  a  cell  with  a  kary- 
okinetic  figure.  X  250. — (Schaper.) 


THE    FEMALE    REPRODUCTIVE    ORGANS.  311 

distinct  membranes — fetal  membranes — the  chorion  and  the  amnion  (Fig. 
232).  The  chorion  lies  next  to  the  decidua  vera  and  is  intimately  united 
with  it.  It  consists  of  two  layers,  an  epithelial  and  a  connective-tissue 
layer,  of  which  the  former  is  turned  toward  the  uterine  wall,  the  latter 
toward  the  amnion.  Two  similar  layers  may  be  distinguished  in  the 
amnion,  but  of  these  the  epithelial  layer,  which  consists  of  cubical  cells, 
is  turned  toward  the  cavity  of  the  uterus,  while  the  connective -tissue 
stratum  faces  the  chorion.  The  amnion  and  chorion  are  loosely  united 
to  each  other  by  mucous  connective  tissue,  in  which  delicate  fibrils  may 
be  seen  extending  from  one  membrane  to  the  other. 

The  lymph-vessels  of  the  uterus  form  in  the  mucosa  a  wide-meshed 
network  provided  with  blind  branches.  From  this  small  stems  proceed 
through  the  muscularis  and  communicate  with  a  close  subserous  network 
of  larger  channels. 

The  nerves  of  the  uterus,  medullated  as  well  as  nonmedullated,  are 
very  numerous.  They  branch — the  medullated  nerves  after  losing  their 
medullary  sheath — in  the  muscularis  and  form  a  dense  plexus  in  this  and 
in  the  mucosa.  From  the  latter  delicate  fibrils  may  be  traced  between 
the  epithelial-cells. 

THE  PLACENTA.* 

The  placenta  is  an  organ  which  from  a  morphologic  standpoint  is 
composed  of  two  heterogeneous  parts,  of  which  the  one  is  produced  by 
the  mother  (placenta  uterina),  the  other  by  the  embryo  (placenta  fcetalis). 
It  is  the  result  of  the  intimate  union  of  a  circumscribed  area  of  the 
chorion  (chorion  frondosum)  with  that  portion  of  the  mucosa  of  the 
uterus  known  as  the  decidua  serotina.  The  placenta  serves  the  purpose 
of  bringing  the  fetal  and  the  maternal  blood  into  the  closest  proximity, 
to  render  possible  the  interchange  of  materials  between  them.  To  sub- 
serve this  function  the  organ  possesses  a  peculiar  histologic  construction, 
in  which  the  blood-vessels,  especially  in  their  arrangement  and  structure, 
take  a  prominent  part. 

In  the  histologic  investigation  of  the  placenta  various  obstacles  are 
encountered,  owing  to  its  being  an  extremely  soft,  spongy  mass,  traversed 
by  numerous  wide  blood-vessels.  The  comprehension  of  the  minute 
structure  will  be  considerably  facilitated  by  proceeding  from  the  pre- 
viously-mentioned fact  that  the  finished  organ  is  the  product  of  two  origi- 
nally heterogeneous  structures,  the  chorion  on  the  one  side,  the  decidua 
serotina  on  the  other,  and  that  their  union  is  substantially  effected  in  that 


This  chapter  is  an  entirely  new  addition  by  the  editor. 


FIG.  234.— SECTION  THROUGH  A  NORMAL  HUMAN  PLACENTA  OK  ABOUT  SEVEN  MONTHS,  IN  SITU. 
Am.,Amnion;  Cho.,  Chorion ;  Vi,  trunk  of  a  villus;  vi,  sections  of  villi  in  the  substance  of  the 
placenta;  D,  decidua  basalis;  Me,  muscularis  ;  D',  compact  layer  of  decidua  ;  Ve,  uterine  artery 
opening  into  the  placenta.  The  fetal  blood-vessels  are  drawn  black  ;  the  maternal  blood-spaces  are 
left  white;  the  chorionic  tissue  is  stippled  except  the  canalized  fibrin,  which  is  shaded  by  lines  ;  the 
remnants  of  the  gland-cavities  in  D'' are  stippled  dark. — (After  Minot.) 

312 


THE  FEMALE  REPRODUCTIVE  ORGANS. 


313 


the  chorion,  by  means  of  numerous  villous-like  proliferations,  penetrates 
the  underlying  serotina,  the  surface  of  which  is  peculiarly  modified  and 
further  regressively  altered  for  its  reception,  and  as  it  were  takes  root  in 
the  same.  For  the  investigation  of  these  relations  sections  through  the 
wall  of  the  uterus  with  the  placenta  in  situ,  toward  the  end  of  pregnancy, 
are  most  instructive.  In  such  a  section  two  sharply-defined  zones  may 
be  recognized  :  an  outer  compact  stratum  consisting  of  the  greatly- 
thickened  muscular  coat  of  the  uterus,  covered  externally  by  the  serosa, 
and  an  inner  spongy  zone  containing  numerous  inter-communicating 
spaces  filled  with  blood.  The  latter  is  the  placenta,  that  is,  the  united 
decidua  serotina  and  chorion  frondosum.  The  accompanying  illustration 
(Fig.  234)  shows  their  relations  under  low  magnification,  which  will  be 
elucidated  by  referring  to  the  schematic  representation  in  Fig.  235. 


Chorionic  villi. 


FIG.  235.—  DIAGRAM  OF  HUMAN  PLACENTA  AT  THE  CLOSE 


Intervillous  spaces. 
Floating  villus. 

}  Attached  villi. 
Vein. 

Spiral  artery. 
Gland. 

Vein. 


REGNANCY.    Comp.  Fig.  234.—  (Schaper.) 


The  surface  of  the  placenta  directed  toward  the  cavity  of  the  uterus 
is  covered  by  a  compact  stratum,  the  mcmbrana  chorii,  which  is  chiefly 
composed  of  fibrillar  connective  tissue,  in  which  the  main  branches  of 
the  umbilical  blood-vessels  run.  The  outer  surface  of  the  chorion  is 
covered  by  a  delicate  membrane,  the  placental  portion  of  the  amnion, 
which  as  previously  stated  consists  of  an  inner  epithelial  and  a  connect- 
ive-tissue layer  and  is  attached  to  the  chorion  by  means  of  embryonic 
connective  tissue.  The  other  surface  of  the  membrana  chorii,  that 
directed  toward  the  wall  of  the  uterus,  is  closely  beset  with  innumerable 
villous-like  structures,  large  and  small,  which  in  the  upper  part  of  the 


HISTOLOGY. 


placenta  form  a  dense  tangle,  the  terminal  ramifications  of  which  are 
embedded  in  the  cleft,  uneven  substance  of  the  serotina.  On  closer 
study  of  this  villous  tangle  it  will  be  seen  that  the  larger  stems  run  a 
more  or  less  direct  course  from  the  chorion  to  the  serotina,  in  order  to 
secure  a  firm  union  with  the  latter,  while  their  many  much-branched 
lateral  twigs  usually  establish  no  connection  with  the  uterine  portion  of 
the  placenta,  but  terminate  free  in  the  blood-spaces,  the  so-called  inter- 
villous  spaces,  between  the  chorion  and  serotina.  Dependent  upon  these 
relations  the  branches  of  the  chorionic  villi  are  divided  into  "roots  of 
attachment"  or  main  stems,  and  free  processes,  or  floating villi.  From  the 
chorion  a  branch  of  the  umbilical  artery  enters  each  main  stalk  and 
within  the  terminal  ramifications  of  the  villus  breaks  up  into  a  dense 


Protoplasmic  coat.  "" 
Epithelial  nucleus. 
Capillaries.  <:i--- 


Cell-patch  (Zellkuoten). 


Small  arterv. 


-•  Cell-patch   (Zellknoten)    in 
process  of  formation. 


Protoplasmic   coat 
(syncytium). 


Capillary. 


Cell-patch  (Zellknoten).     


FIG.  236. — CROSS-SECTION  THROUGH  A  SMALLER  (A)  AND  LARGER  (B)  CHORIONIC  VILLUS  OF  A  HUMAN 
PLACENTA  .AT  THE  END  OK  PREGNANCY.     X  250. — (Schaper.) 

capillary  network  from  which  the  umbilical  veins  take  their  origin  and 
carry  back  the  blood  from  the  chorion  through  the  umbilical  cord  to  the 
fetus.  Accordingly,  the  blood-vessel  system  of  tJie  fetal  placenta  is  entirely 
closed.  Nowhere  does  a  direct  intermingling  of  the  maternal  arid  the  fetal 
blood  occur. 

A  cross-section  of  one  of  the  smaller  chorionic  villi,  highly  magni- 
fied, shows  that  it  is  chiefly  composed  of  mesenchymal  tissue  (mucous 
tissue),  in  which  the  blood-vessels  are  embedded  (Fig.  236).  This 
central  supporting  substance  is  covered  by  an  irregular  and  not  every- 
where continuous  stratum  of  epithelium.  In  the  earlier  months  of 
development  two  distinct  strata  may  be  distinguished  in  the  epithelium 


THE    FEMALE    REPRODUCTIVE    ORGANS.  315 

of  the  villi  :  an  inner,  lying  immediately  upon  the  supporting  tissue,  in 
which  the  cells  possess  large  nuclei  and  definite  contours,  so  that  in  the 
main  they  are  distinctly  separated  from  one  another,  and  an  outer  layer, 
consisting  of  a  continuous  protoplasmic  mass — syncytium — containing 
numerous  small,  irregularly-scattered  nuclei.  Toward  the  end  of 
pregnancy,  however,  the  epithelium  of  the  villi  undergoes  great  altera- 
tion, as  appears  in  the  illustration  (Fig.  236).  On  the  larger  villi  a  true 
epithelial  investment  has  almost  entirely  disappeared  and  instead  isolated 
accumulations  of  large  round  nuclei  are  found  ;  they  stain  intensely,  are 
embedded  in  a  clear,  homogeneous  substance,  and  form  protuberances 
(Zcllknotcn,  cell-patches)  on  the  surface  of  the  villi.  Between  these  cell- 
patches  the  connective-tissue  of  the  villi  frequently  is  covered  only  by  a 
thin,  homogeneous  stratum,  or  in  some  cases  (especially  in  smaller  villi) 
this  stratum  still  retains  more  or  less  the  character  of  the  protoplasm 
containing  scattered  nuclei.  There  are  many  indications  that  the  latter 
is  the  remains  of  the  syncytium,  while  the  cell-patches  probably  origi- 
nated in  the  primitive  inner  stratum  of  the  epithelium  of  the  villi.  In 
many  places  the  syncytium  is  transformed  into  a  peculiar  hyaline  sub- 
stance permeated  by  fissures,  which  often  lies  upon  the  chorion  in  dense 
strata  and  is  called  canalized  fibrin* 

The  histologic  structure  of  the  maternal  portion  of  the  placenta — 
placenta  ntcrina — in  its  essential  features  has  been  described  in  connec- 
tion with  the  decidua  in  the  preceding  chapter.  But  certain  peculiarities, 
as  well  as  the  union  of  maternal  and  fetal  placenta  in  a  functional  whole 
require  a  brief  consideration. 

The  placental  portion  of  the  decidua  (Fig.  234),  that  forming  the 
lower  stratum  of  the  placenta  (basal  plate),  is  greatly  thinned  (from  o.  5 
to  i  mm.),  but  as  in  the  extraplacental  portion  an  upper  compact 
layer  and  a  lower  cavernous  layer  (gland-lumina)  may  be  distinguished. 
The  decidual  cells  are  extremely  numerous  and  lie  closely  crowded.  A 
honey-combed  structure  of  connective-tissue  septa  (septa  placentas]  arises 
from  the  surface  of  the  serotina,  directed  toward  the  intervillous  spaces, 
and  penetrates  between  the  villi  of  the  chorion,  separating  the  latter  into 
lobes  or  cotyledons.  Only  in  the  peripheral  regions  of  the  placenta  do 


*  It  has  not  been  yet  determined  with  certainty  whether  the  epithelium  of  the  villi  of  the 
human  placenta  is  entirely  derived  from  the  epithelium  of  the  chorion,  or  whether  the  epi- 
thelium of  the  serotina  participates  in  its  composition.  Recent  investigations,  however,  as  well 
as  comparative  anatomical  facts,  indicate  that  only  the  inner  epithelial  stratum  of  the  villi 
comes  from  the  chorionic  epithelium,  while  the  syncytium  is  derived  directly  from  the  mucosa 
of  the  uterus,  the  epithelium  of  which,  on  the  ingrowth  of  the  chorial  villi,  becomes  closely 
applied  to,  and  blends  with,  the  epithelium  of  the  latter. 


3l6  HISTOLOGY. 

these  septa  reach  to  the  membrana  chorii,  where  frequently  they  form 
on  the  inferior  surface  of  the  latter  a  thin  membranous  stratum,  the 
decidua  placentalis  subchorialis.  On  the  margin  of  the  placenta  the 
serotina  gradually  increases  in  thickness  and  passes  into  the  vera,  at 
which  point  it  is  closely  applied  to  and  firmly  united  with  the  chorion. 
Within  the  area  of  the  placenta,  however,  the  chorion  and  serotina  are 
far  apart  and  the  space  between  them  is  filled  with  the  above-described 
chorial  villi  and  the  blood  circulating  between  them  ;  it  is  maternal 
blood  that  surrounds  the  villi  on  all  sides  and  is  thus  brought  into  the 
closest  relation  with  the  fetal  circulation. 

Of  especial  interest  is  the  behavior  of  the  blood-vessels  within  the 
placenta  uterina  (Fig.  234  and  Fig.  235).  Numerous  arteries  from  the 
muscularis  of  the  uterus  penetrate  the  serotina,  in  which  they  make  cork- 
screw-like tours  during  the  course  of  which  they  lose  their  muscular  coat 
and  continue  as  wide  tubes  consisting  alone  of  the  lining  endothelium. 
Near  the  surface  of  the  decidua  they  usually  bend  sharply  at  right  angles 
and  then  open  directly  into  the  intervillous  spaces  of  the  placenta.* 
Noivliere  do  the  arteries  break  up  into  capillaries.  The  veins  (likewise 
endothelial  tubes,  though  wider  than  the  arteries)  also  are  in  direct  com- 
munication with  the  placental  spaces  ;  they  enter  the  decidua  usually 
under  a  very  narrow  angle,  run  more  or  less  parallel  to  the  surface,  and 
unite  in  the  deeper  strata  in  a  wide  venous  plexus.  In  accordance  with 
the  description  of  these  conditions  of  the  vessels,  the  arteries  and  veins 
within  the  serotina  can  no  longer  be  recognized  by  the  histologic 
structure  of  their  walls,  but  can  only  be  distinguished  by  their  width  and 
their  course.  The  arteries  in  addition  usually  are  characterized  by  a 

*In  regard  to  the  relation  of  the  decidual  blood-vessels  to  the  intervillous  spaces  there  are 
two  conflicting  theories.  According  to  the  one  the  intervillous  spaces  are  independent  clefts 
without  proper  walls,  that  are  formed  in  the  course  of  development  between  the  fetal  and 
maternal  portions  of  the  placenta,  with  which  the  blood-vessels  opening  on  the  surface  of 
the  decidua  are  in  direct  communication.  Accordingly  the  villi  of  the  chorion  are  in  direct 
contact  with  the  maternal  blood  circulating  in  these  spaces.  The  opposite  view  regards  the 
blood-spaces  of  the  placenta  as  the  enormously- widened  capillaries  of  the  decidua,  which, 
during  the  mutual  process  of  intergrowth  between  the  placenta  uterina  and  placenta  foetalis,  the 
developing  villi  of  the  chorion  have  invaginated.  According  to  this  the  blood-vessel  system  of 
the  decidua  is  closed  and  the  arteries  and  veins  communicate  through  a  system  of  capillary 
lacunae  (the  intervillous  spaces).  Further,  the  chorial  villi  are  not  directly  bathed  in  the 
maternal  blood,  but  are  separated  from  it  by  a  thin  stratum  of  cells,  the  capillary  endothelium, 
which  lies  directly  upon  them.  Recent  investigations  of  Keibel  apparently  support  the  latter 
view,  since  in  a  human  placenta  in  an  early  stage  of  development  he  succeeded  in  tracing  the 
endothelium  of  the  decidual  blood-vessels  into  the  intervillous  spaces  and  demonstrating  it  as  a 
continuous  stratum  on  the  surface  of  the  chorionic  villi.  It  is  possible  that  in  the  further  de- 
velopment of  the  placenta  this  endothelial  covering  undergoes  regressive  change,  so  that  in  later 
stages  it  cannot  as  a  rule  be  demonstrated. 


THE    FEMALE    REPRODUCTIVE    ORGANS.  317 

thin,  homogeneous,  enveloping  stratum  that  stains  intensely  with  carmine, 
in  which  a  few  scattered  nuclei  are  found.  This  peculiar  layer  is  prob- 
ably a  product  of  the  degenerated  muscular  coat. 


THE  VAGINA  AND  THE  GENITALIA. 

The  vagina  is  formed  by  a  mucous  membrane,  a  muscular  tunic, 
and  a  fibrous  tunic. 

The  mucous  membrane  is  composed  of  a  stratified  scaly  epithelium 
and  a  tunica  propria  beset  with  papillae,  that  is  built  up  of  small,  inter- 
lacing bundles  of  connective  tissue  and  contains  a  few  elastic  fibers  and 
a  varying  quantity  of  leucocytes.  The  latter  occasionally  exist  in  the 
form  of  solitary  nodules  ;  in  this  case  numerous  migrating  leucocytes  are 
found  in  the  epithelium  in  these  localities.  The  mucosa  rests  on  a  sub- 
mncosa,  which  is  composed  of  loosely-united  connective-tissue  bundles 
and  robust  elastic  fibers.  Glands  are  absent  within  the  vaginal  mucous 
membrane. 

The  muscular  coat  comprises  an  inner  circular  and  an  outer  longi- 
tudinal layer  of  smooth  muscle-fibers. 

The  outer  fibrous  tunic  is  a  dense  connective-tissue  structure,  rich  in 
elastic  fibers. 

The  blood-  and  lymph-vessels  are  arranged  in  parallel  horizontal  net- 
works in  the  submucosa  and  in  the  tunica  propria.  Between  the  bundles 
of  the  muscular  tunic  lies  a  close  network  of  wide  venous  channels. 
The  nerves  form  a  plexus  in  the  outer  fibrous  tunic,  beset  with  many 
small  ganglia. 

The  mucous  membrane  of  the  external genitalia  in  the  vicinity  of  the 
clitoris  and  the  urethral  orifice  differs  from  the  vaginal  mucosa  in  the 
possession  of  numerous  mucous  glands,  from  0.5  to  3  mm.  in  size,  anjd 
on  the  labia  minora  in  the  presence  of  sebaceous  follicles  (without  hair- 
follicles)  from  0.2  to  2  mm.  in  size.  The  clitoris  repeats  on  a  diminutive 
scale  the  structure  of  the  penis  ;  end-bulbs  and  tactile  corpuscles  occur 
in  the  glans. 

The  large  glands  of  the  vestibule  (Bartholin)  are  the  homologues  of 
the  glands  of  Cowper  in  the  male. 

The  labia  majora  are  folds  of  the  integument  and  possess  the  same 
structure. 

The  acid  vaginal  secretion  contains  desquamated  scaly  epithelial- 
cells  and  leucocytes,  and  not  infrequently  an  infusorium,  trichomonas 
vaginalis. 


3l8  HISTOLOGY. 


TECHN1C. 

No.  140. — For  a  general  view  of  the  testicle  make  a  transverse 
incision  *  through  the  testicle  and  epididymis  of  a  newborn  child  ;  fix 
the  pieces  in  about  50  c.c.  of  Kleinenberg's  picrosulphuric  acid  (p.  21) 
and  harden  in  30  c.c.  of  gradually -strengthened  alcohol  (p.  33).  Stain 
thick  transverse  sections  of  the  entire  organ  in  dilute  carmine  (p.  36),  and 
in  Hansen's  hematoxylin  (p.  36),  and  mount  in  damar.  Examine  with  very 
low  magnification  (Fig.  214).  In  the  testicle  of  the  rabbit,  cat,  and  dog 
the  corpus  Highmori  is  not  at  the  margin  but  in  the  center  of  the  organ. 

No.  141. — Minute  Structure  of  the  Seminiferous  Tubules. — Place 
small  pieces  (2  cm.  cubes)  of  the  fresh  testicle  of  an  ox  in  200  c.c.  of 
Zenker's  fluid  (p.  31),  and  harden  them  in  50  c.c.  of  gradually-strength- 
ened alcohols  (p.  33).  Cut  sections  as  thin  as  possible,  stain  them  in 
Hansen's  hematoxylin  (p.  36),  and  mount  in  damar  (p.  45).  Even  with 
the  low  power  tubules  in  a  condition  of  activity  can  be  distinguished  from 
resting  tubules  ;  the  former  may  be  recognized  by  the  intensely  blue 
heads  of  the  young  spermatozoa  (Fig.  215). 

No.  142. — Still  better  preparations  are  obtained  by  placing  the  entire 
testicle  of  a  mouse  in  10  c.c.  of  the  platinum-acetic-osmic  acid  mixture 
(p.  33)  for  twenty -four  hours  for  fixation,  then  washing  it  for  several  hours 
in  running  water  and  placing  it  in  20  c.c.  of  gradually-strengthened  alco- 
hols for  hardening.      Mount  the  unstained  sections  in  damar  (Fig.  216). 
The  platinum-acetic-osmium  mixture  does  not  pene 
jl  trate  sufficiently  into  the  testicles   of  larger  animals, 

//I  which  therefore  are  not  suitable. 

No.  143. — Elements  of  tlie  Testicle. — Place  pieces 
about   I   cm.  in  size  of  the  fresh  testicle  of  an  ox  in 
20  c.c.  of  one-third  alcohol  (p.  20)  and  in  five  or  six 
hours  tease  the  tubules  in  a  drop  of  the  same  alcohol. 
Stain   under  the   cover-glass   with  picrocarmine   and 
mount  in  dilute  glycerol.      Several  preparations  from 
FIG.  237.— ISOLATED     different  parts  of  the  organ  should   be  completed  and 
o?     then  not  infrequently  the  cells  of  Sertoli  with  attached 
spermatocytes,  or  the  seminal  filaments  produced  by 
blast.'"  '</,  immature     them,  will  be  obtained  (Fig.  237,  b\ 

seminal   filament;    e, 

ESS"  No.  144.—  Elements  of  the  Semen.— Make  an  in- 

cision into  a  fresh  epididymis  f  and  place  one  drop  of 
the  milk-white  fluid  that  exudes  from  the  cut  surface  on  a  clean  slide  ; 
add  one  drop  of  salt  solution,  apply  a  cover-glass,  and  examine  with  the 
high  power.  After  a  time  let  one  drop  of  distilled  water  flow  under  the 


*If  no  incision  is  made  into  the  organ,  it  does  not  harden  sufficiently,  because  the  dense 
tunica  albuginea  retards  the  penetration  of  the  fluids. 

t  For  a  view  of  the  spiral  fiber  mentioned  above  (p.  293,  remark),  that  can  be  seen  only 
with  very  powerful  immersion  lenses,  I  recommend  the  seminal  filaments  of  the  rat;  they  are 
to  be  examined  in  water. 


THE    FEMALE    REPRODUCTIVE    ORGANS.  319 

cover-glass  ;  the  movements  of  the  spermatozoa  soon  cease  ;  the  heads 
of  the  majority  of  the  seminal  filaments  then  present  their  broad  surface 
and  the  tail  curves  and  forms  a  loop  (Fig.  217,  3).  Remnants  of  proto- 
plasm still  adhere  to  seminal  filaments  not  fully  matured.  The  sperma- 
tozoa may  be  preserved  by  allowing  the  semen  diluted  with  water  to  dry 
on  the  slide  ;  then  apply  a  cover-glass  and  secure  it  with  cement  (p.  45). 
In  examining  such  preparations,  too  much  illumination  gives  rise  to 
troublesome  reflections. 

No.  145. — The  vitality  of  the  seminal  filaments  has  led  to  investiga- 
tions for  forensic  purposes.  For  example,  it  may  be  a  question  as  to 
whether  spots  occurring  on  a  linen  garment  were  produced  by  semen. 
Cut  strips  from  5  to  10  mm.  long  from  the  suspected  spots,  soak  them 
for  from  five  to  ten  minutes  in  a  watch-glass  containing  distilled  water,  and 
tease  a  few  fibers.  With  the  high  power  (500  :  i)  chiefly  examine  the 
edges  of  the  isolated  linen  fibers,  to  which  the  seminal  filaments  if  present 
are  attached.  Not  infrequently  the  heads  are  broken  off;  they  are  recog- 
nized by  their  peculiar  luster,  their  shape,  and  their  (in  man  small)  size. 

No.  146. — Seminal  Filaments  of  the  Frog. — The  male  frog  is  recog- 
nized by  a  well-developed  wart  on  the  ball  of  the  thumbs.  Open  the 
abdominal  cavity ;  the  testicles  are  a  pair  of  oval  bodies  (similar  to  the 
kidneys  of  mammals)  lying  to  either  side  of  the  vertebral  column.  Divide 
the  organ  by  a  transverse  incision  ;  dilute  a  drop  of  the  fluid  with  a  drop 
of  salt  solution.  The  seminal  filaments  are  large,  the  head  thin  and 
elongated,  the  tail  so  delicate  that  at  the  first  glance  it  may  be  overlooked. 
Immature  filaments  lie  grouped  in  tufts. 

No.  147. — Epididymis,  Ductus  Defer  ens,  and  Seminal  Vesicles. — 
Pieces  from  I  to  2  cm.  in  size  are  to  be  fixed  in  about  100  c.c.  of  Zenker's 
fluid  and  hardened  in  60  c.c.  of  gradually-strengthened  alcohol  (p.  33). 
Stain  the  sections  with  Hansen's  hematoxylin  and  mount  in  damar  (Fig. 
218,  219,  220). 

No.  148. — The  prostate  and  the  different  divisions  of  the  male 
urethra  are  to  be  prepared  in  2  or  3  cm.  cubes  like  No.  147  (Fig.  221). 

No.  149. — The  Ovary. — The  ovaries  of  small  animals  may  be  fixed 
in  toto  and  those  of  larger  animals  with  several  incisions  transverse  to 
the  long  axis  in  100  or  200  c.c.  of  Zenker's  fluid  (p.  31)  and  hardened 
in  100  c.c.  of  gradually-strengthened  alcohol  (p.  33).  For  a  topo- 
graphical view  (Fig.  222)  it  is  advisable  to  cut  thick  sections,  because 
otherwise  the  contents  of  the  follicles  easily  fall  out.  Not  every  section 
includes  large  follicles  ;  it  is  often  necessary  to  cut  many  sections,  in  order 
to  strike  a  favorable  place.  Stain  the  sections  with  Hansen's  hematoxylin 
(p.  36),  or  in  bulk  with  borax-carmine  (p.  37).  Mount  in  damar  (p.  45). 

No.  150. — Fresh  ova  may  be  obtained  as  follows.  Procure  the 
fresh  ovaries  of  a  cow.  The  large  Graafian  follicles  are  transparent,  pea- 
sized  vesicles,  which  with  the  scissors  may  be  easily  shelled  out  in  toto. 
Transfer  the  isolated  follicle  to  a  slide  and  prick  it  with  a  needle.  The 
needle  must  be  carefully  thrust  in  on  the  side  of  the  follicle  lying  against 
the  slide,  otherwise  the  liquor  will  spurt  out  and  carry  the  ovum  with  it. 


32O  HISTOLOGY. 

With  the  low  power,  and  without  placing  a  cover-glass  on  the  prepara- 
tion, search  for  the  ovum,  which  surrounded  by  the  cells  of  the  cumulus 
ovigerus  will  be  found  in  the  escaping  liquor  folliculi  (Fig.  226,  A). 
Place  two  narrow  strips  of  paper  on  either  side  of  the  ovum,  carefully 
apply  a  cover-glass,  and  examine  with  the  high  power. 

The  beginner  will  sacrifice  many  a  follicle  before  he  succeeds  in 
finding  an  ovum.  Often  the  ovum  does  not  escape  when  the  follicle  is 
pricked ;  it  may  then  be  found  by  teasing  the  follicle. 

No.  151. — Ova  of  the  Frog. — Place  a  small  piece  of  the  fresh  ovary 
of  a  frog  on  a  slide  and  prick  all  the  large  pigmented  eggs,  so  that  their 
contents  escape.  Place  that  which  remains  in  a  watch-glass  with  dis- 
tilled water  and  wash  it  by  moving  it  to  and  fro  with  needles.  Place  the 
watch-glass  on  a  black  background  ;  the  smaller,  still  unpigmented  folli- 
cles can  then  be  seen.  Transfer  the  washed  object  to  a  clean  slide,  apply 
a  cover-glass,  and  examine  it.  The  ova  have  very  large  germinal  vesi- 
cles ;  the  germinal  spot  disappears  early,  and  usually  is  not  to  be  seen. 
On  the  other  hand,  a  dark  spot  occurs  in  the  vitellus,  the  "  nucleus  of 
the  vitellus."  Surrounding  the  ovum  is  a  finely-striated  membrane,  the 
inner  surface  of  which  is  covered  with  flat  cells  ;  this  is  the  theca  folliculi 
with  the  simple  follicular  epithelium. 

No.  152. — The  Oviducts. — Pieces  i  or  2  cm.  long  are  to  be  fixed  in 
50  c.c.  of  3  per  cent,  nitric  acid  and  after  five  hours  hardened  in  60  c.c. 
of  gradually-strengthened  alcohol.  Stain  with  Hansen's  hematoxylin 
and  mount  in  damar. 

No.  153. — For  topographical  preparations  of  the  human  uterus  the 
uteri  of  young  individuals  are  suitable.  According  to  its  size,  fix  the 
whole  uterus  or  pieces  of  it  2  cm.  square  in  about  100  c.c.  of  Zenker's 
fluid  (p.  31)  and  harden  in  100  c.c.  of  gradually-strengthened  alcohol 
(p.  33).  Stain  in  Hansen's  hematoxylin  and  in  eosin  (p.  37)  and  mount 
in  damar  (p.  45).  (Fig.  228.)  In  such  preparations  the  gland  follicles 
are  often  very  indistinct.*  In  the  two-horned  uteri  of  many  animals 
the  often  greatly-convoluted  gland-tubules  can  be  more  readily  distin- 
guished ;  the  arrangement  of  the  muscular  strata  is  different,  •  more 
regular  than  in  the  human  organ. 

No.  1 54. — For  preparations  of  the  human  uterine  mucosa,  cut 
out  pieces  I  cm.  square  and  treat  them  after  No.  153.  Owing  to  the 
extreme  tortuousness  of  the  glands,  sections  contain  only  fragments  of 
the  follicles.  The  cilia  can  seldom  be  seen  in  fixed  preparations. 

No.  155. — The  placenta  is  to  be  treated  according  to  No.  154-f 
Before  cutting  sections  the  pieces  must  be  embedded  in  celloidin  or 
paraffin  ;  in  the  latter  case  the  sections  must  be  fastened  to  the  slide  (see 
Microtome  Technic,  Preservation  of  Sections),  in  order  that  the  innumer- 
able branches  of  the  villi,  cut  in  every  plane,  do  not  fall  out.  The  study 
of  preparations  of  this  kind  is  one  of  the  most  difficult  tasks  of  the  micro- 
scopist. 

*  Fig.  228  was  sketched  from  an  unstained  preparation.  The  glands  were  not  so  distinct 
as  they  appear  in  the  illustration. 

f  Fixation  in  absolute  alcohol  often  yields  very  good  results. 


X.  THE  SKIN  AND  ITS  APPENDAGES. 

The  skin  is  principally  composed  of  connective  tissue,  which  how- 
ever is  nowhere  exposed,  but  is  protected  by  a  continuous  epithelial  coat 
The  connective-tissue  portion  of  the  skin  is  called  corium,  dermis,  or  true 
skin,  the  epithelial  portion,  epidermis  or  cuticle.  The  appendages  of  the 
skin,  the  nails  and  the  hairs,  as  well  as  the  glands  and  the  hair-follicles 
embedded  within  the  corium,  are  products  of  the  epidermis. 


THE  SKIN. 

The  surface  of  the  corium  is  marked  by  many  fine  furrows,  which 
intersect  and  enclose  rectangular  or  lozenge-shaped  areas  or  run  parallel 
between  minute  ridges.  The  lozenge-shaped  areas  may  be  seen  on  the 
surface  of  the  greater  part  of  the  body,  while  the  ridges  are  confined  to 
the  volar  surface  of  the  hand  and  the  plantar  surface  of  the  foot.  The 
areas  and  ridges  are  beset  with  numerous  conical  elevations,  the  papilla, 
the  number  and  size  of  which  vary  greatly  in  different  regions  of  the 
body.  The  largest  (up  to  0.2  mm.  high)  and  most  numerous  papillae 
occur  on  the  palm  of  the  hand  and  on  the  sole  of  the  foot ;  they  are  very 
slightly  developed  in  the  skin  of  the  face. 

The  corium  chiefly  consists  of  interlacing  connective-tissue  bundles, 
mingled  with  elastic  fibers,  cells,  and  smooth  muscle-fibers.  In  the  super- 
ficial strata  of  the  corium  the  connective-tissue  bundles  are  delicate  and 
are  united  in  a  closely-interwoven  texture  ;  in  the  deeper  strata  they  are 
larger  and  intersecting  at  sharp  angles  form  a  coarse-meshed  network. 
These  differences  have  led  to  the  recognition  of  two  strata  in  the  corium, 
a  superficial  stratum  beset  with  papillae,  stratum  papillare,  and  a  deep 
stratum,  stratum  reticulare.  There  is  no  sharp  demarcation  between  the 
two  strata,  the  one  gradually  blending  with  the  other  (Fig.  238).  The 
stratum  reticulare  is  connected  with  an  underlying  network  of  loosely- 
united  bundles  of  fibrous  tissue,  the  wide  meshes  of  which  contain  clusters 
of  fat-cells  ;  this  is  the  stratum  subcutaneum.  The  storing  of  much 
adipose  tissue  in  the  interfascicular  spaces  of  this  stratum  leads  to  the 
formation  of  the  panniculus  adiposus.  The  tissue  of  the  subcutaneous 
21  321 


322 


HISTOLOGY. 


stratum  is  firmly  or  loosely  connected  with  the  fibrous  sheaths  of  the 
muscles  (the   fasciae)  or  with  the  periosteum  of  the  bones.     The  elastic 


Epi: 

dermis. 


Stratum  corneum. 


Stratum  lucidum. 
Stratum  germinativum. 


f      Stratum  papillare. 


' 


Corium.  - 


Excretory  duct. 


Stratum  reticulare. 


Coil-gland. 


Stratum  subcutaneum. 


FIG.  238.— VERTICAL  SECTION  OF  THE  SKIN  OF  THE  FINGER  OF  ADULT  MAN.    X  25.    With  this  magnifi- 
cation the  stratum  granulosum  is  not  visible.    Techn.  No.  156. 

fibers,  which  are  thin  in  the  stratum  papiHare  and  thicker  in  the  stratum 
reticulare,  form  networks  uniformly  distributed  throughout  the  corium. 
The  cells  include  spindle-shaped  and  plate-like  connective-tissue  elements, 


Depressions  in  which  the 
apillas  were  inserted. 


Furrow  corresponding  to 
a  ridge  of  the  corium. 


Portion  of  the  duct  of 
a  coil-gland. 


FIG.  239. — EPIDERMIS  FROM  THE  SKIN  OF  THE  DORSUM  OF  THE  HUMAN  FOOT,  SEEN  FROM  THE  LOWER 
SURFACE.  X  120.  The  preparation  is  so  to  speak  the  cast,  while  the  surface  of  the  corium  beset 
with  papillae  represents  the  matrix.  Techn.  No.  157. 

leucocytes,    and    fat-cells.       The    number    of   the   cellular   elements    is 
extremely  variable.     The  muscle-fibers  almost  exclusively  belong  to  the 


THE   SKIN    AND    ITS    APPENDAGES.  323 

non-striped  variety  and  the  majority  are  attached  to  the  hair-follicles  ; 
only  in  a  few  situations  in  the  body  do  they  occur  spread  out  in  the  skin 
(tunica  dartos,  nipple).  Striated  muscle-fibers  occur  in  the  skin  of  the 
face,  where  they  radiate  from  the  mimetic  muscles. 

The  epidermis  consists  of  a  stratified  squamous  epithelium,  in  which 
at  least  two  sharply-defined  zones  may  be  distinguished  :  a  deep  zone, 
the  stratum  germinativum  (Malpighi),  which  fills  the  depressions  occur- 
ring between  the  papillae  of  the  corium,  and  a  superficial,  firmer  zone,  the 
stratum  corneum.  Both  strata  exclusively  consist  of  epithelial-cells, 
which  exhibit  different  appearances  in  the  separate  layers.  In  the  deepest 
layer  of  the  stratum  germinativum  the  cells  are  cylindrical  and  possess 
oblong  nuclei ;  these  are  followed  by  several  layers  of  spherical  cells  that 
are  beset  with  numerous  minute  thorns,  the  prickle-cells.  The  thorns 
are  delicate  thread-like  processes,  which  penetrate  the  small  amount 
of  intercellular  cement-substance  occurring  between  the  cells  and  unite 
neighboring  cells  to  one  another.  Therefore  they  are  called  intercellular 
bridges  (Fig.  14).  In  the  stratum  germinativum  new  cells  are  continually 
being  formed  by  indirect  division. 

The  stratum  corneum  is  not  everywhere  of  the  same  structure ; 
two  types  may  be  distinguished  :  (i)  In  localities  where  the  epidermis  is 
well  developed,  as  on  the  palm  of  the  hand  and  the  sole  of  the  foot,  a 
stratum  of  eel  Is  characterized  by  highly-refracting  granules  (keratohyalin 
granules)  lies  next  to  the  stratum  germinativum.  The  granules  are  pro- 
duced by  the  cornification  of  some  parts  of  the  cell-protoplasm.*  This 
stratum  is  named  stratum  granulosum.  In  the  next  layer  the  granules 
dissolve,  blend  with  the  parts  of  the  protoplasm  not  yet  transformed  into 
horny  substance,  and  form  a  uniformly  clear  zone,  the  stratum  lucidum. 
This  is  covered  by  the  broad  stratum  corneum  proper.  In  this  stratum 
all  the  noncornified  parts  of  the  cell  under  the  influence  of  the  atmos- 
phere are  desiccated  ;  so  it  happens  that  each  cell  contains  a  delicate, 
horny  mesh-work,  and — since  the  intercellular  bridges  also  become 
cornified — is  enveloped  in  a  horny  membrane.  The  nucleus  desiccates  ; 
the  space  which  is  occupied  persists  for  a  long  period.  These  partly 
cornified,  partly  desiccated  cells  are  only  slightly  flattened.  (2)  In  situ- 
ations where  the  epidermis  is  thinner,  over  the  remaining  surface  of  the 
skin,  the  stratum  granulosum  is  narrow  and  interrupted.  The  stratum 
lucidum  is  absent.  The  horny  cells  of  the  stratum  corneum  are  extremely 
flattened  and  are  united  in  lamellae.  The  last  trace  of  the  nucleus  is  lost. 


*  These  granules  dissolve  in   a   solution  of  potassium   hydroxid  and  therefore  are  not 
composed  of  keratin,  which  is  insoluble  in  this  reagent. 


324  HISTOLOGY. 

The  surface  of  the  horny  stratum  undergoes  a  continual  physiologic 
desquamation  ;  the  resulting  loss  is  compensated  by  the  pushing  upward 
of  the  growing  elements  of  the  germinal  stratum. 

The  color  of  the  skin  is  due  to  the  deposition  of  fine  granules  of 
pigment  between  and  within  the  cells  of  the  deeper  layers  of  the  epider- 
mis ;  only  in  certain  localities,  for  example,  in  the  vicinity  of  the  anus, 
are  pigmented  connective-tissue  cells  found  in  the  adjacent  corium. 

With  regard  to  the  source  of  the  pigment  of  the  epidermis  there  are 
two  theories,  of  which  the  one  attributes  its  origin  to  the  connective 


Part  of  the  stratum 
corneum. 


Stratum  lucidum. 

:-='  t£r~f —     Stratum  granulosum. 
$gfe 

'/#i^ 

/  ...;•••  ;'v$:' 


...  .-  •        • 

*$  Stratum  germinativum. 


—  Part  of  the  papillary  layer 
of  corium. 


'    ' 


FIG.  240.  —  FROM  A  SECTION  THROUGH  THE  SKIN  OF  THE  SOLE  OF  THE  FOOT  OF  ADULT  MAN. 

X  360.   Techn.  No.  156. 

tissue,  the  other  to  the  epithelium.  According  to  the  first,  hitherto 
frequently  accepted  opinion,  the  so-called  "transportation"  theory, 
the  pigment  is  carried  to  the  epithelium  by  pigmented  connective-tissue 
cells,  that  wander  from  the  corium  into  the  epidermis  and  there  dis- 
integrate. In  the  human  hair-bulb  pigmented  forms  presenting  great 
diversity  in  outline  are  found  between  the  epithelial  elements  ;  some  of 
these  figures  are  cells,  but  it  has  not  been  demonstrated  with  certainty 
that  they  are  connective-tissue  cells,  others  are  not  cells,  but  intercellular 
clefts  filled  with  pigment.  The  second  theory  is  supported  by  the 
developmental  history,  which  teaches  that  the  pigment  originates  in  the 


THE    SKIN    AND    ITS    APPENDAGES. 


325 


epithelium  of  the  hair  without  the  intervention  of  connective-tissue  cells. 
The  pigment  of  the  retina  also  is  certainly  and  exclusively  of  epithelial 
origin. 

THE    NAILS. 

The  nails  are  horny  laminae,  which  rest  upon  the  nail-bed,  a  special 
modification  of  the  skin.  The  nail-bed  is  bounded  on  the  sides  by  the 
nail-walls,  a  pair  of  sloping  folds  with  the  descent  forward.  The  nail- 
bed  and  nail-wall  embrace  a  furrow,  the  nail-groove,  in  which  the  lateral 
borders  of  the  nail  are  inserted  (Fig.  241).  The  posterior  border  of  the 
nail,  the  nail-root,  rests  in  a  similar  but  deeper  groove,  the  matrix*  in 
which  the  principal  growth  of  the  nail  takes  place. 

The  anterior  free  border  of  the  nail  projects  over  the  nail-ridge,  a 
small  seam-like  prominence  at  the  distal  end  of  the  nail-bed. 

The  nail-bed  consists  of  corium  and  of  epidermis.      The  fibre-elastic 


Nail. 


Eponychium. 


{Corium. 
Epithe- 
lium. 

Nail-wall. 


Nail-groove. 

Bone  of  third 
phalanx. 

FIG.  241.— DORSAL  HALF  OF  A   CROSS-SECTION  OF  THE  THIRD  PHALANX  OF  A  CHILD.    X  15. 
ridges  of  the  nail-bed  in  cross-section  appear  like  papillae.     Techn.  No.  158. 


The 


bundles  of  the  corium  partly  are  disposed  parallel  to  the  long  axis  of  the 
finger,  partly  run  vertically  from  the  periosteum  of  the  phalanx  to  the 
surface.  The  surface  of  the  corium  does  not  possess  papillae,  but  minute 
longitudinal  ridges.  They  begin  low  at  the  matrix,  increase  in  height 
toward  the  anterior  border  of  the  nail,  and  terminate  abruptly  at  the 
point  where  the  latter  leaves  its  bed.  The  epithelium  is  of  the  stratified 
scaly  variety,  of  the  same  structure  as  that  of  the  germinal  stratum  of 
the  epidermis.  It  covers  the  ridges  of  the  nail-bed,  fills  up  the  furrows 
between  them,  and  is  sharply  defined  from  the  substance  of  the  nail. 
The  matrix,  likewise,  consists  of  corium  and  epidermis  ;  the  corium  is  dis- 
tinguished by  its  tall  papillae,  the  stratified  scaly  epithelium  is  very  thick 
and  is  not  sharply  defined  from  the  nail-substance,  but  gradually  blends 


*  Some  authors  name  the  whole  nail-bed  matrix,  which  is  in  a  measure  justified  by  the 
growth  in  thickness  of  the  nail  that  occurs  here. 


326  HISTOLOGY. 

with  the  latter.  This  is  the  place  where  by  continual  division  of  the 
epithelial-cells  the  material  for  the  growth  of  the  nail  is  furnished.  On 
this  account  the  epithelium  is  called  the  germ-layer  of  the  nail.  The 
extent  of  the  matrix  is  indicated  by  the  lunula,  a  white 
anteriorly-convex  area,  visible  to  the  unaided  eye  ;  it 
is  produced  by  the  thick,  uniformly-extended  germ- 
layer.  The  nail-wall  exhibits  the  usual  structure  of 
the  skin.  The  germinal  stratum  of  the  nail-wall 
gradually  blends  with  the  epithelium  of  the  nail-bed  ; 
the  horny  stratum  extends  into  the  nail-groove  and  as 
FIG.  242.  —  ELEMENTS  "  eponychium  "  covers  a  small  portion  of  the  border 

OF  HUMAN  NAIL.    X  r  .,     .  ..... 

240.  Techn.No.i58a.      of  the  nail,  but  soon  diminishes  in  thickness  and  dis- 
appears (Fig.  241). 

The  nail  itself  consists  of  horny  epithelial  scales,  that  are  very 
firmly  united  with  one  another  and  are  distinguished  from  the  horny 
cells  of  the  stratum  corneum  of  the  epidermis  by  the  possession  of  a 
nucleus  (Fig.  242).* 

THE  HAIRS  AND  THE  HAIR-FOLLICLES. 

The  hairs  are  flexible,  elastic,  horny  threads,  which  are  distributed 
over  nearly  the  entire  surface  of  the  body  and  on  the  integument  of  the 
cranium  are  united  in  small  groups.  The  part  of  the  hair  which  projects 
beyond  the  free  surface  of  the  skin  is  called  the  shaft ;  the  portion 
obliquely  embedded  within  the  integument,  the  root ;  this  at  its  lower 
extremity  is  expanded  to  a  hollow  knob,  the  hair-bulb,  which  is  occupied 
by  a  formation  of  the  corium,  the  hair  papilla  (Fig.  243). 

Each  hair- root  is  inserted  in  the  hair-follicle,  a  modification  of  the 
skin  in  the  formation  of  which  corium  and  epidermis  participate ;  the 
parts  furnished  by  the  latter  are  named  the  epithelial  root-sheaths,  the 
portion  originating  from  the  corium,  the  dermal or  connective -tissue  sheath. 
From  two  to  five  glands,  the  sebaceous  glands,  open  laterally  into  the 
upper  part  of  the  follicle.  Bundles  of  smooth  muscle-fibers,  the  arrec- 
tores  pilorum,  pass  obliquely  from  the  upper  surface  of  the  corium  and 
attach  themselves  beneath  a  sebaceous  gland  to  the  fibrous  sheath  of  the 
hair-follicle  ;  the  point  of  insertion  of  these  fibers  is  always  on  the  side 
toward  which  the  hair  inclines  and  forms  an  acute  angle  with  the  free 
surface  of  the  skin  ;  consequently  .when  they  contract,  the  follicle  and 
the  shaft  become  erect. 

*The  new  anatomic  nomenclature  reckons  the  epithelium  of  the  nail-bed  to  the  nail,  that 
according  to  this  representation  consists  of  stratum  corneum  and  stratum  germinativum. 


THE    SKIN    AND    ITS    APPENDAGES. 


327 


The  hair  consists  entirely  of  epithelial-cells,  which  are  arranged  in 
three  well-defined  strata  :  (i)  theV#/&/f,  which  covers  the  surface  of  the 
hair  ;  (2)  the  cortical  substance,  which  forms  the  chief  bulk  of  the  hair  ; 
(3)  the  medulla,  which  occupies  the  axis  of  the  hair. 

The  cuticle  consists  of  transparent  imbricated  scales  :  horny  epithelial- 
cells  without  nuclei. 

The  cortical  substance  of  the  shaft  consists  of  elongated  horny 
epithelial-cells  with  attenuated  nuclei,  which  are  very  intimately  united 
with  one  another  ;  on  the  root  the  cells  become  the  softer  and  rounder, 
their  nucleus  correspondingly  the  more  spherical,  as  they  approach  the 
hair-bulb. 

The   medulla  is   absent   in   many  hairs  ;  when  it   is  present  (in   the 


Hair-shaft. 

Hair-root. 
Sebaceous  gland. 

Arrector  pili  muscle. 

Root-sheaths. 

Connective-tissue  hair-    - 
follicle. 

Hair-bulb. 

Hair-papilla.  — 

Fat-cells.  

FIG.  243.— FROM  A  THICK  CROSS-SECTION  OF  HUMAN  SCALP.    X  20.    Techn.  No.  161. 

thicker  hairs)  it  does  not  extend  through  the  entire  length  of  the  hair. 
It  consists  of  cubical,  finely-granular  epithelial-cells,  which  contain  a 
rudimentary  nucleus  and  are  usually  disposed  in  twofold  rows. 

The  colored  hairs  contain  pigment,  diffused,  and  in  the  form  of 
granules,  which  partly  occur  between  and  partly  within  the  cells  of  the 
cortical  substance.*  In  every  hair  which  has  attained  its  full  develop- 
ment extremely  minute  air-vesicles  occur  ;  they  are  found  in  the  cortical 
substance  as  well  as  in  the  medulla,  and  also  in  the  intercellullar  clefts. 


*  As  to  the  source  of  the  pigment,  see  page  324. 


328 


HISTOLOGY. 


The  follicle  of  finer  (lanugo)  hairs  is  formed  alone  by  the  epidermal 
root-sheaths,  but  in  coarser  hairs  the  corium  participates  in  its  construction. 
In  the  follicles  of  the  latter  the  following  strata  may  be  distinguished  : 
an  outer  longitudinal  stratum  formed  of  loosely-united,  longitudinally- 
disposed  bundles  of  connective  tissue,  mingled  with  elastic  fibers  and 
richly  supplied  with  blood-vessels  and  nerves  ;  next  follows  a  middle 
circular  stratum,  thicker,  consisting  of  small  fibrous  bundles  circularly 
arranged,  which  is  contiguous  to  an  inner  clear,  homogeneous  belt,  the 
glassy  or  hyaline  membrane,  resembling  in  character  the  elastic  membranes. 
Elastic  fibers  do  not  occur  in  the  middle  layer  nor  in  the  papilla.  These 


Cortical  substance.    _ 


Medullary  substance.    \ 


Cuticle.     ~ 


« \.  P 


FIG.  244. — ELEMENTS  OF  A  HUMAN  HAIR  AND  HAIR-FOLLICLE.  X  240.  i.  White  hair;  2,  scales  of  the 
cuticle;  3,  cells  of  the  cortical  substance  of  the  shaft;  4,  cells  of  Huxley's  layer;  5,  cells  of  Henle's 
layer  having  the  appearance  of  a  fenestrated  membrane ;  6,  cells  of  the  cortical  substance  of  the  root. 
Techn.  No.  159  a  and  No.  160. 

three  strata  are  derived  from  the  corium  and  together  named  the  dermal 
or  connective-tissue  hair-follicle.  Within  the  hyaline  membrane  lies  the 
outer  root-sheath,  which  as  a  continuation  of  the  germ-layer  of  the 
epidermis  consists  of  stratified  scaly  epithelium ;  inward  to  this  lie 
continuations  of  the  stratum  granulosum  and  stratum  corneum,  which 
extend  about  to  the  point  where  the  ducts  of  the  sebaceous  glands  open 
into  the  follicle  ;  immediately  below  (toward  the  papilla)  the  inner  root- 
sheath  begins  abruptly,  which  in  the  lower  portion  of  the  follicle  is 
differentiated  into  two  sharply-defined  layers.  The  outer  of  these  two, 
Henle's  layer,  consists  of  a  single  or  double  row  of  epithelial-cells 


THE   SKIN    AND    ITS    APPENDAGES. 


329 


without  nuclei  (here  and  there  an  atrophic  nucleus  is  present),  while  the 
inner,  Huxley 's  layer,  is  formed  of  a  simple  stratum  of  nucleated  cells. 
The  inner  surface  of  this  layer  is  lined  by  a  delicate  membrane,  the 
cuticle  of  tJic  root-sheath^  which  exhibits  the  same  structure  as  the  cuticle 
of  the  hair.  Toward  the  base  of  the  follicle  the  outer  root-sheath 
diminishes  in  thickness  and  disappears  ;  the  elements  of  the  inner  root- 


XX         '•**' 


Connective- 

tissue 
hair-follicle. 


Inner  root- 
sheath. 


Hair. 


f  Longitudinal  fibrous 

layer. 
J   Circular  fibrous  laver. 


Glassy  membrane. 

Outer  root-sheath. 
Henle's  layer. 

Huxley's  layer. 
Sheath  and  hair-cuticle. 
Cortical  substance. 
Medullary  substance. 


FIG.  245.— FROM  A  HORIZONTAL  SECTION  OF  HUMAN  SCALP.    Y.  240.    Cross-section  of  a  hair  and 
follicle  in  the  lower  half  of  the  root.     Techn.  No.  161. 


hair- 


sheath,  as  well  as  those  of  the  cuticulae,  all  become  nucleated  cells,  that 
can  be  distinguished  as  separate  layers  until  near  the  neck  of  the  papilla  ; 
there  they  lose  their  sharp  demarcation  and  gradually  coalesce  with  one 
another,  but  nevertheless  can  be  distinguished  from  the  cells  of  the  hair- 
bulb  by  the  pigmentation  of  the  latter.* 

DEVELOPMENT  OF  THE  HAIR. 

The  first  anlage  of  the  hair  and  of  the  hair-follicle  appears  at  the 
end  of  the  third  embryonal  month,  in  the  form  of  a  local  thickening  of 
the  epidermis,  which  is  chiefly  effected  by  elongation  of  the  (columnar) 
cells  of  the  deepest  layer  of  the  germinal  stratum.  This  thickening 
grows  in  length  down  into  the  corium  (Fig.  246,  A)  and  forms  a  solid 
epidermal  peg,  the  hair-germ  (Fig.  246,  A,  B),  that  at  its  lower  end 


*  Already  at  the  level  of  the  papilla  keratohyalin  granules  appear  in  the  cells  of  Henle's 
layer,  at  a  somewhat  higher  level  also  in  those  of  Huxley's  layer,  that  a  little  farther  up 
disappear ;  from  this  upwards  the  elements  of  the  inner  root-sheath  are  corneous. 


330 


HISTOLOGY. 


becomes  expanded  and  club-shaped  (Fig.  246,  C).  Meanwhile  the 
papilla  (C,  p)  and  the  dermal  portion  of  the  hair-follicle  (C,  hb)  develop 
by  differentiation  of  the  connective  tissue  of  the  surrounding  corium. 
The  hair-germ  separates  into  an  outer  stratum  and  into  an  inner  axial 
cord  (D,  s).  The  former  becomes  the  outer  root-sheath  (aw),  the 


FIG.  246.— FROM  A  VERTICAL  SECTION  (A)  OF  THE  SKIN  OF  THE  CHEEK  OF  A  FOUR  MONTHS'  HUMAN 
EMBRYO  AND  (B,  C,  D)  OF  THE  SKIN  OF  THE  FOREHEAD  OF  A  HUMAN  EMBRYO  FIVE  AND  A 
HALF  MONTHS  OLD.  X  80.  E.  Epidermis,  consisting  throughout  of  nucleated  epithelial-cells ; 
C,  corium  ;  x,  thickening  ;  hk,  hair-germ  ;  hb,  connective-tissue  hair-follicle  ;  /.papilla;  azu,  outer 
root-sheath  ;  s,  axial  portion,  in  which  in  the  upper  division  the  separation  into  (iw)  inner  root-sheath 
and  (fi)  hair  is  visible  ;  t,  anlage  of  the  sebaceous  glands.  Techn.  No.  162. 

peripheral  portion  of  the  axial  strand  becomes  the  inner  root-sheath 
(iw),  the  central  part,  the  hair  (//).  The  sebaceous  glands  arise  as 
local  outgrowths  of  the  outer  root-sheath  (t). 

The  development  of  hairs  in  the  manner  described  may  occur  after 
birth  and  until  late  in  life. 

GROWTH  OF  THE  HAIR  AND  OF  THE  ROOT-SHEATHS. 

The  growth  of  the  hair,  of  the  cuticular  sheaths,  and  of  the  inner 
root-sheath  takes  place  by  continual  mitotic  division  of  the  epithelial 
elements  around  the  papilla,  that  becoming  horny  annex  themselves 
from  below  to  previously  cornified  cells.  Therefore  the  tip  is  the  oldest, 
the  portion  lying  immediately  above  the  hair-bulb  the  youngest,  part  of 
the  hair.  The  outer  root-sheath,  on  the  other  hand,  grows  in  a  radial 
direction  from  the  inner  surface  of  the  glassy  membrane  towards  the  axis 
of  the  hair. 

SHEDDING  AND  REPLACEMENT  OF  HAIR. 

After  birth  all  the  hairs  are  shed  and  replaced  by  others.  In  the 
adult  a  constant,  but  not  periodic,  replacement  of  the  dead  hairs  of  the 


THE    SKIN    AND    ITS    APPENDAGES.  331 

scalp  and   beard  occurs.     (With   regard   to   the   shedding  of  the  other 
hairs  nothing  is  definitely  known.) 

The  minute  details  of  the  process  are  as  follows  :  the  hair-bulb 
becomes  horny  and  frayed,  like  a  brush  ;  the  now  dead  hair  pushes 
upward  from  the  papilla,*  the  empty  root-sheaths  collapse,  while  at  their 
inferior  extremity  lies  the  papilla,  atrophied  and  altered  in  form  (Fig. 
247).  After  a  (often  long)  period  the  epithelial  elements  of  the  empty 


Dead  hair.    v          Iff/J^  £''' ^il  '  Sebaceous  gland. 

U  / 

-!£»•• 

Empty  root-sheath.  — — jHfef  ^Jf'-'J^^i^^ 


Hair-papilla. 

f**^  ,-£.;;•/       .!*£$        .'  ^.,s 

<?<;        *'•$?_*  3*.- Dead  hair. 

"    .  i^:' 

•'•'".( :''-i' -'^tf'i^ '•"•'•  ~   Empty  root-sheath. 

.  '•"''    ' 

-    Hair-papilla. 

FIG.  247. — FROM  A  VERTICAL  SECTION  OF  THE  HAIRY  SCALP  OF  ADULT  MAN.     X  40.    Techn.  No.  163. 

root-sheaths  begin  to  grow  and  form  a  new  hair-germ,  from  which  the 
new  hair  develops  by  the  same  processes  as  the  embryonal  hair.  The 
new  hair  thus  formed  pushes  itself  upward  under  and  beside  the  effete 
hair,  while  the  latter  after  a  shorter  or  longer  period  falls  out. 

THE  GLANDS  OF  THE  SKIN. 

The  sebaceous  glands  are  either  unbranched  or  branched  simple 
saccular  glands.  Each  gland  consists  of  a  short  excretory  duct  (Fig. 
248,  A,  a)  and  of  a  variable  number  of  little  gland-sacs  (/).  The  duct 
is  lined  by  stratified  scaly  epithelium,  an  extension  of  the  outer  root- 

*  Further  growth  of  the  cornified  hair  does  not  occur ;  the  ascent  is  passive  and  de- 
pendent on  the  multiplication  of  the  non-cornified  epithelial-cells  lying  under  the  dead  hair. 


332 


HISTOLOGY. 


sheath,  which  by  a  gradual  decrease  in  the  number  of  its  layers  passes 
into  the  epithelial  lining  of  the  gland-sacs.  This  at  the  beginning 
consists  of  low  cuboidal  cells  (Fig.  248,  £),  that  toward  the  interior  are 
followed  by  spherical  or  polyhedral  elements  varying  in  size,  which  fill 
the  entire  gland-sac  and  exhibit  all  the  transitional  phases  in  the  process 
by  which  the  cell  is  converted  into  the  secretory  product  of  the  gland 
(Fig.  248,  2,  3,  4).  The  secretion,  the  sebum,  during  life  is  a  semifluid 
substance  that  consists  of  fat  and  disintegrated  cells.  While  the  seba- 
ceous glands  occur  as  appendages  of  the  hair-follicles  of  the  coarser 
hairs  (Fig.  243),  in  the  case  of  the  lanugo  hairs  reversed  relations  pre- 
vail, since  the  follicles  of  the  latter  appear  as  the  appendages  of  the 
powerfully-developed  sebaceous  glands  (Fig.  248,  A).  The  sebaceous 


Epidermis.  / '  ~ 

\AJ .:£S 


Corium.  / 


Cell  with  shrunken 
nucleus. 


Cell  with  well-de- 
veloped drops  of 
secretion. 


Cell  with  develop- 
ing drops  of  se- 
cretion. 

Cubical  cells. 

FIG.  248. — A.  FROM  A  VERTICAL  SECTION  THROUGH  THE  ALA  NASI  OF  A  CHILD.  X  40.  C.  Stratum  cor- 
neum ;  M,  stratum  germinativum ;  t,  sebaceous  gland  consisting  of  four  follicles,  a,  duct  of  the 
same  ;  w,  lanugo  hair,  about  to  be  shed,  h,  hair-follicle  of  the  same,  at  the  base  of  which  a  new  hair, 
x,  is  forming. 

B.  FROM  A  VERTICAL  SECTION  OF  THE  SKIN  OF  THE  ALA  NASI  OF  AN  INFANT.  X  240.  Follicles  of  a 
sebaceous  gland  containing  gland-cells  in  various  stages  of  secretion.  Techn.  No.  164. 


glands  are  distributed  with  the  hairs  over  the  entire  body  and. are  wanting 
only  where  they  are  absent,  on  the  palm  of  the  hand  and  on  the  sole  of 
the  foot.  There  also  are  sebaceous  glands  that  are  not  associated  with 
hair- follicles  ;  for  example,  on  the  red  edge  of  the  lips,  on  the  labia 
minora,  on  the  glans,  on  the  prepuce  of  the  penis  ;  in  the  latter  situa- 
tion they  are  known  as  glandule?  prczputiales  (Tyson).  The  sebaceous 
glands  are  always  situated  in  the  superficial  layers  of  the  corium,  in  the 
stratum  papillare.  Their  size  varies  from  0.2  to  2.2  mm.  ;  the  latter  are 
found  in  the  integument  of  the  nose,  where  their  excretory  ducts  are 
visible  to  the  unaided  eye. 

The  coil-glands  (sudoriparous  or  sweat-glands)  are  long,  unbranched 
tubules,  that  at  their  lower  ends  are  rolled  into  a  spherical  coil  having  a 


THE   SKIN    AND    ITS    APPENDAGES.  333 

diameter  of  0.3  to  7  mm.  (of  the  latter  size  in  the  axilla).  Two  parts 
are  distinguished,  the  excretory  duct  and  the  coil  (Fig.  238).  The  duct 
runs  a  straight  or  sinuous  course  through  the  corium,  enters  the  epidermis 
between  two  papillae,  through  the  stratum  corneum  of  which  it  is  spir- 
ally twisted,  and  opens  on  the  surface  of  the  skin  by  a  rounded  orifice, 
the  sweat-pore,  just  visible  to  the  naked  eye.  The  walls  of  the  duct 
consist  of  longitudinally-disposed  bundles  of  connective  tissue,  lined 
within  by  several  layers  of  cubical  epithelial-cells.  The  coil  is  a  greatly- 
convoluted  simple  canal,  the  walls  of  which  are  formed  of  a  simple  layer 
of  cubical  cells,  containing  granules  of  pigment  and  of  fat,  surrounded 
by  a  delicate  membrana  propria.  In  well-developed  glands  longitudinally- 
disposed  smooth  muscle-fibers  occur  between  the  membrana  propria  and 
the  gland-cells.  Branched  tubules  have  been  observed  only  in  the 
axillary  and  circumanal  glands. 

The  secretion  usually  is  an  oily  fluid  substance,  for  the  purpose  of 
lubricating  the  skin  ;  only  under  the  influence  of  disturbed  in  nervation 
do  the  coil-glands  discharge  the  watery  liquid  called  sweat.  The  coil- 
glands  are  distributed  over  the  entire  surface  of  the  skin  and  are  absent 
only  on  the  glans  and  on  the  inner  surface  of  the  prepuce.  They  are 
most  numerous  in  the  skin  of  the  palm  of  the  hand  and  of  the  sole  of 
the  foot. 

THE  BLOOD-VESSELS,  LYMPH-VESSELS,  AND  NERVES  OF 

THE  SKIN. 

The  arteries  of  the  skin  originate  in  a  network  lying  above  the  fasciae 
and  branch  as  they  pass  toward  the  surface  of  the  skin.  These  branches 
anastomose  with  one  another  and  with  those  of  neighboring  arteries  and 
in  the  lower  stratum  of  the  corium  form  a  horizontally-disposed  network, 
the  cjctaneous  netivork.  The  arteries  supplying  the  skin  are  therefore 
not  end-arteries.* 

From  this  network  two  capillary  territories  are  supplied  ;  the  deeper 
is  intended  for  the  adipose  tissue  (Fig.  249,  af),  the  more  superficial 
appears  in  the  form  of  basket-like  plexuses  surrounding  the  coil-glands 
(a"}.  From  the  cutaneous  network  twigs  ascend  that  anastomose  and 
form  a  second  horizontal  network  in  the  upper  third  of  the  corium,  the 
snbpapillary  plexus ;  from  this  very  small  twigs  arise,  which  run  for  a 
short  distance  along  the  rows  of  papillae  and  send  little  branches  into 

*"  End-arteries"  are  those  small  arteries  which  do  not  anastomose  with  neighboring 
arteries,  but  independently  supply  capillary  circuits  of  varying  extent.  When  they  become 
obstructed  the  part  of  the  organ  which  they  supply  die-. 


334 


HISTOLOGY. 


them  (Fig.  249,  a'").  These  smallest  twigs  do  not  anastomose  with  one 
another,  hence  are  end-arteries.  The  branches  for  the  hair-follicles  and 
sebaceous  glands  also  arise  from  the  subpapillary  plexus. 

The  blood  returning  from  the  capillaries  of  the  papillae,  the  hair- 
follicles,  and  the  sebaceous  glands  is  taken  up  by  veins  that  form  a  dense 
horizontal  plexus  lying  beneath  the  papillae  and  that  occasionally  are 
united  with  a  second  horizontal  plexus  lying  close  below  the  first.  From 
this  plexus  small  venous  trunks  descend  beside  the  arteries  and  lead  to 
a  third  network  lying  in  the  lower  half  of  the  corium,  which  is  not  so 


Stratum  subcutaneum. 


FIG.  249.— FROM  A  VERTICAL  SECTION  OF  THE  SKIN  OF  THE  SOLE  OF  A  HUMAN  FOOT.  X  50-  sc, 
Stratum  corneum  ;  sg,  stratum  germinativum  ;  a,  artery;  v,  vein  ;  a'  v',  branches  to  the  panniculus 
adiposus ;  a'1  v" ,  branches  to  the  coil-glands  ;  k,  duct  of  the  same  ;  vx,  vein  accompanying  the  duct. 
Techn.  No.  165. 

evenly  spread  out  as  those  preceding.  This  plexus  takes  up  the  veins 
coming  from  the  coil-glands  and  then  those  proceeding  from  the  lobules 
of  adipose  tissue.  It  should  further  be  noted  that  a  branch  of  the  veins 
of  the  coil-glands  passes  along  the  excretory  duct  to  the  venous  plexus 
of  the  stratum  papillare  (Fig.  249,  v  x)  and  that  the  hair-papilla  receives 
an  independent  arterial  branch.  From  the  third  venous  network  larger 
veins  lead  to  the  lower  boundary  of  the  skin,  where  a  fourth  horizontally- 
disposed,  "  subcutaneous "  venous  network  occurs,  from  which  still 


THE   SKIN    AND    ITS    APPENDAGES.  335 

larger  trunks  turn  into  the  subcutaneous  tissue  and  then  unite  with  the 
large  subcutaneous  veins,  some  of  which  are  provided  with  names.  The 
lymph-vessels  form  two  horizontal  capillary  networks,  of  which  that  con- 
sisting of  smaller  channels  and  narrower  meshes  lies  in  the  papillary 
stratum  of  the  corium  beneath  the  vascular  network  ;  the  other,  wider- 
meshed,  is  situated  in  the  subcutaneous  tissue.  Special  networks  of  lymph- 
capillaries  surround  the  hair-follicles,  the  sebaceous  and  coil-glands. 

The  nen>es  of  the  integument  (numerous  in  the  palm  of  the  hand 
and  the  sole  of  the  foot)  partly  terminate  in  the  subcutaneous  tissue  in 
lamellar  corpuscles  ;  partly  they  end  in  tactile-corpuscles,  in  tactile-cells, 
and  as  intra-epithelial  fibrils  (Fig.  122).  The  hairs  are  also  supplied  with 
nledullated  nerve-fibers,  which  run  up  to  the  point  where  the  sebaceous 
glands  open  into  hair-follicles  ;  here  they  divide,  lose  their  medullary 
sheath,  and  as  naked  axis-cylinders,  usually  running  longitudinally,  ter- 
minate in  a  spoon-shaped  expansion  on  the  glassy  membrane  (epilemmal 
nerve-ending)  ;  in  the  tactile-hairs  (sensory  hairs)  of  animals  delicate 
twigs  arise  from  these  nerves,  which  pass  through  the  hyaline  membrane 
of  the  hair-follicle  into  the  outer  root-sheath  and  there  end  in  tactile- 
discs.  The  hair-papilla  does  not  possess  nerves.  In  regard  to  the 
nerves  of  the  coil-glands,  see  page  243. 


THE    MAMMARY  GLANDS. 

The   mammary  gland   consists   of  from   fifteen   to  twenty   tubular 
glands,  which  are  held  together  and  united  in  a  common   body  by  loose 
connective  tissue  containing  fat-cells.      Each  of  these  glands  has  its  own 
excretory  duct  opening  on  the  nipple,  that 
shortly  before  its  termination  is  provided  with 
a  conspicuous  spindle-shaped  expansion,  the 
ampulla  or  sinus  lactiferus,  and  by  means  of 
dichotomous  ramifications  is  connected  with 
the   terminal  compartments.     The  latter  lie 
close  together  and  are  united  by  connective 
tissue  into  small  lobules. 

The  excretory  ducts  are  composed  of  a     FIG.  25o.-FROM  A  THIN  CROSS- 

.  ....  ....  ,  SECTION       OF      THE      MAMMARY 

Columnar     epithelium,     Which     in     the     larger          GLAND  OF  A  PREGNANT  RABBIT. 

X  240.   /,  Fat  in  the  gland-cells; 

branches  not  infrequently  is  replaced  by  a  >»•  membrana.propria.  Techn. 
stratified  scaly  epithelium,  surrounded  by  a 

membrana  propria,  outside  of  which  are  fibrous  bundles  which  are  in 
general  circularly  disposed.  The  gland-tubules  are  lined  by  a  simple 
layer  of  epithelial-cells  the  height  of  which  varies  greatly  ;  they  are  low 


336  HISTOLOGY. 

when  the  tubules  are  filled,  cubical  or  columnar  when  the  tubules  are 
empty.  In  the  latter  case  the  cells  contain  globules  of  fat.  The  gland- 
ular elements  rest  upon  a  membrana  propria  composed  of  cells  (p.  81), 
which  is  enveloped  by  loose  connective  tissue  intermingled  with  varying 
numbers  of  leucocytes  and  plasma-cells. 

After  lactation  is  ended  a  gradual  regressive  metamorphosis  occurs, 
that  is  indicated  by  abundant  development  of  the  interlobular  connective 
tissue.  The  lobules  become  smaller,  the  tubules  begin  to  atrophy.  In 
elderly  persons  all  the  lobules  and  tubules  disappear  and  only  the 
excretory  ducts  remain. 

In  children  of  both  sexes  the  mammary  gland  chiefly  consists  of 
connective-tissue,  within  which  the  branched  excretory  ducts,  their  ends 
terminating  in  a  bulbous  enlargement,  are  enclosed.  Tubules  are 


FIG.  251. — FROM  A  THICK  SECTION  OF  THE  MAMMARY  GLAND  OF  A  WOMAN  LAST  PREGNANT  Two 
YEARS  BEFORE.  X  50.  i.  Large  excretory  duct;  2,  small  excretory  duct;  3,  gland-lobules,  separ- 
ated from  one  another  by  connective  tissue.  Techn.  No.  166. 

wanting.  The  mammary  gland  of  the  adult  male  exhibits  the  same 
structure. 

In  the  adult  female  before  pregnancy  has  occurred  the  mammae  are 
disc-shaped  bodies,  that  principally  consist  of  connective  tissue  and  of 
the  excretory  ducts.  Only  a  few  gland-tubules  at  the  extremites  of  the 
smallest  branches  of  the  ducts  are  present. 

The  integument  of  the  nipple  and  of  the  areola  is  characterized  by 
deep  pigmentation,  by  tall  papillae,  and  by  the  presence  of  smooth 
muscle-fibers,,  which  latter  partly  are  circularly  arranged  around  the 
orifices  of  the  galactophorous  ducts,  partly  vertically  to  the  apex  of  the 
nipple.  The  pigmentation  is  due  to  the  presence  of  pigment-granules  in 
the  deepest  layers  of  the  epidermis.  In  the  integument  of  the  areola 
accessory  mammary  glands,  the  areolar  glands  (Montgomery)  occur. 


THE    SKIN    AND    ITS    APPENDAGES.  337 

The  blood-vessels  approach  the  mammae  from  all  sides  and  form 
capillary  networks  embracing  the  gland-tubules.  The  lymph-vessels  form 
capillary  plexuses  lying  within  and  between  the  gland-lobules.  Lym- 
phatic networks  also  occur  in  the  vicinity  of  the  ampullae  and  theareolae. 

The  nerves  are  in  part  distributed  to  the  blood-vessels,  in  part 
behave  like  those  of  the  salivary  glands  (p.  243). 

Microscopically  milk  consists  of  a  clear  fluid,  the  milk  plasma,  in 
which  milk~givbules}  from  2  to  5  it  in  size,  are  suspended.     Owing  to  the 
fact  that  the  globules  do  not  coalesce,  the 
presence  of  a  delicate  membrane  of  casein  ° 

is  assumed.      In    addition,  isolated    cells  1   /  r  ;;w;  / 

enclosing  oil-globules  (leucocytes  ?  )  are         A 
found  in  milk.  O 

c.°    & 

The  elements   of  the  milk   secreted      o°  0  c° 
before    and    in   the    first    few    days    after 
parturition  include,  beside  the  milk-glob- 

ules,    the     SO-Called     COlostnim-COrpUSCleS,        FlG.  252._^.  MILK-GLOBULES  FROM  Hu- 

nucleated   cells,   some   of  which   contain        ^JS^^f^SSlSiSS^ 

,,  1111  A  PREGNANT  WOMAN.    X  560.    i.  Cell 

minute    yellow-colored     and    larger    un-        containing  uncoiored  fat-giobuies  ;  2, 

cell     containing    minute    colored    fat- 
fat-drOpletS,     Others     Only     UllCOl-      •      globules;    3,   leucocyte;    4,    milk-gloh- 


ules.     Techn.  No.  168  a. 

ored  fat-droplets. 

The  mode  in  which  the  glandular  epithelium  participates  in  the  for- 
mation of  the  milk-globules  and  the  colostrum-corpuscles  is  not  yet  alto- 
gether clear.  Only  this  much  is  known  with  certainty,  that  the  cells  do 
not  perish  in  the  act  of  secretion.  It  is  a  question  whether  the  fat  con- 
tained within  the  glandular  cells  is  discharged  alone  or  with  the  portion 
of  the  cell  directed  toward  the  lumen  of  the  tubule. 


TECHNIC. 

No.  156. — Strata -of  the  Skin  ;  Coil-glands. — Cut  from  the  pad  of 
the  finger,  the  palm  of  the  hand,  or  the  sole  of  the  foot  pieces  of  skin, 
as  fresh  as  possible,  from  i  to  2  cm.  square  together  with  a  thin  stratum 
of  the  subjacent  fat  and  place  them  in  30  c.c.  of  absolute  alcohol.  To 
prevent  curling  of  the  pieces  pin  them  on  a  small  cork-plate  with  the 
epidermis  turned  toward  the  cork,  and  place  the  whole  in  absolute 
alcohol.  On  the  following  day  remove  the  pieces  from  the  cork-plate  and 
place  them  for  from  three  to  four  weeks  in  50  c.c.  of  90  per  cent,  alcohol. 
Cut  thin  and  thick  sections.  The  latter  are  indispensable  in  order  to  see 
the  excretory  ducts  of  the  coil-glands  in  their  entire  length.  The  most 
suitable  for  this  purpose  is  the  skin  of  the  sole  of  the  foot  of  children, 
because  the  still  short  ducts  of  the  coil-glands  here  run  vertically  (Fig. 
238).  Stain  with  alum  carmine,  ten  minutes  (p.  36) ;  the  red  coils  can 

22 


33^  HISTOLOGY. 

be  seen  with  the  unaided  eye ;  mount  in  damar.  Examine  with  the  low 
power.  In  thick  sections  the  papillae  often  are  indistinct,  because  they 
are  encircled  by  the  red-colored  stratum  germinativum,  the  screw-like 
twisted  ends  of  the  excretory  ducts  may  be  most  distinctly  seen  when 
the  object  is  faintly  illuminated  or  with  oblique  illumination  (see  p.  50, 
remark  *). 

To  render  the  stratum  granulosum  visible,  bulk-staining  with  borax- 
carmine  for  two  or  three  days  (p.  37),  is  to  be  recommended.  The 
granules  of  this  stratum  are  then  stained  an  intense  red  (Fig.  240). 

No.  157. — Pretty  preparations  of  the  under  surface  of  the  epidermis 
are  obtained  by  fixation  of  shreds  of  the  epidermis  of  the  dorsum  of  the 
foot,  that  can  often  be  detached  from  injected  cadavers,  in  30  c.c.  of 
absolute  alcohol.  Stain  for  two  minutes  in  Hansen's  hematoxylin  and 
mount  in  damar  (Fig.  239). 

No.  158. — For  preparations  of  the  nails  fix  the  distal  phalanx  of  a 
child  from  eight  to  twelve  years  of  age  (in  adults,  that  of  the  little  finger, 
if  possible  of  women),  two  or  four  weeks  in  100  or  200  c.c.  of  Miiller's  fluid 
and  harden  in  about  100  c.c.  of  gradually-strengthened  alcohol ;  decalcify 
(P-  33)  5  harden  again  and  stain  thick  cross-sections  ten  minutes  in  alum- 
carmine  (p.  36).  (Fig.  241.)  In  cutting  sections  place  the  knife  on  the 
volar  side  (not  on  the  nail  side)  of  the  phalanx.  The  substance  of  the 
nail  frequently  shows  differently-colored  strata.  In  the  nails  of  old 
cadavers  the  epithelium  often  becomes  loosened  from  the  ridges. 

No.  1 58  a. — Elements  of  the  Nails. — Place  pieces  of  nail  i  or  2  mm. 
broad  in  a  test-tube  containing  5  c.c.  of  concentrated  potash-lye  and 
heat  it  over  a  flame  until  it  boils  up  once.  Transfer  the  nail  with  a  drop 
of  the  lye  to  a  slide  and  scrape  off  some  of  the  softened  surface  ;  apply 
a  cover-glass.  On  examination  with  a  high  power,  cells  will  be  found 
like  those  in  Fig.  242.  For  comparison,  investigate  the  horny  cells  of 
the  stratum  corneum,  which  may  be  obtained  by  lightly  scraping  the 
pad  of  the  finger  with  the  handle  of  a  scalpel.  Examine  the  polygonal 
scales  in  a  drop  of  distilled  water,  with  a  high  power. 

No.  159. — Hairs. — Place  a  hair  in  a  drop  of  salt  solution  on  a  slide 
and  examine  it  with  the  low  and  the  high  power  ;  the  most  suitable  for 
study  are  white  hairs  and  the  hairs  of  the  beard.  The  hair  cuticle  of 
man  is  very  delicate  and  the  transverse  markings  produced  by  the  imbri- 
cation of  the  cells  are  often  very  indistinct ;  usually  only  fine  wavy  lines 
are  visible.  The  hairs  of  many  animals,  on  the  other  hand,  show  the 
cuticula  very  well,  for  example,  sheep's  wool. 

No.  i  59  a. — For  the  demonstration  of  the  elements  of  the  hairs,  place 
a  piece  of  hair  i  or  2  cm.  long  in  a  drop  of  pure  sulphuric  acid  on  a  slide 
and  apply  a  cover-glass  ;  press  lightly  on  the  cover-glass  with  a  needle 
and  the  cortical  substance  will  split  up  into  fibers,  which  consist  of 
adherent  cortical  cells.  Slightly  warm  the  slide,  press  again  with  a 
needle,  so  that  the  cover-glass  becomes  slightly  displaced  ;  numerous 
free  elements,  superficial  scales  and  cortical  cells,  will  then  be  seen. 


THE    SKIN    AND    ITS    APPENDAGES.  339 

No.  1 60. — For  the  exhibition  of  the  elements  of  the  hair-follicles  (and 
the  hairs)  cut  from  a  mustachioed  human  upper  lip  a  piece  2  cm.  square 
and  place  it  in  dilute  acetic  acid  (5  c.c.  of  acetic  acid  to  100  c.c.  of  dis- 
tilled water).  In  two  days  the  individual  hairs  with  their  sheaths  can  be 
easily  withdrawn  and  their  elements  separated  by  teasing  in  a  drop  of 
distilled  water  (Fig.  244).  The  cells  of  Henle's  sheath  float  in  small 
complexes  in  the  preparation  and  closely  resemble  fenestrated  membranes 
(Fig.  244,  5).  The  fenestra  are  spaces  normally  occurring  between 
Henle's  cells,  through  which  processes  of  the  cells  of  Huxley's  stratum 
extend  to  the  outer  root-sheath.  Not  infrequently  a  hair-follicle  is 
obtained  at  the  base  of  which  a  new  hair  is  developing  (similar  to  Fig. 
247)- 

No.  161. — For  the  study  of  hairs  and  hair-follicles  place  pieces  2  or 
3  cm.  square  of  the  fresh  skin  of  the  scalp  in  about  200  c.c.  of  a  2.5 
per  cent,  solution  of  potassium  bichromate .  (p.  21,  9)  for  from  four  to 
eight  weeks  ;  wash  them  from  one  to  three  hours  in  running  water  and 
harden  in  the  dark  in  about  100  c.c.  of  gradually-strengthened  alcohol. 
Longitudinal  sections  which  include  the  entire  length  of  the  follicle  are 
very  difficult  to  cut.  Macroscopic  orientation  as  to  the  direction  of  the 
hair  is  first  necessary.  To  obtain  preparations  like  that  in  Fig.  243  thick 
sections,  unstained,  are  to  be  mounted  in  glycerol.  Thin  sections  usu- 
ally include  only  a  portion- of  the  hair-follicle.  It  is  much  easier  to  cut 
thin  cross-sections,  but  care  must  be  taken  to  make  the  cut  vertical  to 
the  longitudinal  direction  of  the  hair,  not  parallel  to  the  surface  of  the  skin. 
In  this  way  a  single  section  shows  different  levels  of  hairs  and  hair- 
follicles  ;  such  sections  are  to  be  stained  in  dilute  carmine  (p.  36),  and 
Hansen's  hematoxylin,  or  better,  first  with  hematoxylin  and  then  with 
picrocarmine  (p.  36)  ten  minutes,  and  mounted  in  damar.  Especially 
instructive  are  the  sections  through  the  hair-follicle  close  to  the  hair-bulb 
(Fig.  245). 

No.  162. — For  the  development  of  hair  cut  pieces  about  2  cm.  square 
of  the  skin  of  the  forehead  (not  of  the  hairy  scalp)  of  a  five-  or  six- 
months'-old  human  embryo  ;  span  them  out  (see  No.  156) ;  place  them 
for  fourteen  days  in  100  or  200  c.c.  of  Muller's  fluid  and  harden  in  about 
100  c.c.  of  gradually-strengthened  alcohol.  Stain  the  tissue  in  bulk  in 
borax-carmine  (p.  37).  The  sections  may  also  be  stained  in  Hansen's 
hematoxylin  (p.  36).  Embed  the  tissue  in  liver ;  endeavor  to  cut  sec- 
tions exactly  in  the  direction  of  the  hair-follicle,  which  is  much  more 
easily  done  than  in  the  hairy  scalp  of  the  adult.  Mount  in  damar. 
The  sections  exhibit  all  stages  of  development  (Fig.  246).  The  epithe- 
lial thickenings  are  only  to  be  seen  in  well-preserved  epidermis,  which  in 
embryos  is  often  somewhat  macerated.  They  are  more  easily  found  in 
embryos  of  the  lower  animals. 

No.  163. — Shedding  and  Replacement  of  Hair. — The  eyelids  of 
newborn  children  are  most  suitable.  Treat  like  No.  184.  Cut  sagittal 
sections.  Vertical  sections  of  the  hairy  scalp  often  yield  good  results 
(Fig-  247). 


34O  HISTOLOGY. 

No.  164. — The  Sebaceous  Glands. — Fix  and  harden  the  alae  nasi  of 
newborn  children  in  100  c.c.  of  a  2.5  per  cent,  solution  of  potassium 
bichromate  (like  No.  161).  Cut  thick  and  thin  sections;  stain  them 
with  dilute  carmine  (p.  36),  and  with  Hansen's  hematoxylin  (p.  36),  and 
mount  in  damar.  Sections  lengthwise  to  the  dorsum  of  the  nose  often 
show  sebaceous  glands  and  hair-follicles,  but  they  must  be  exactly 
vertical  (Fig.  248).  The  alae  of  the  nose  of  adults,  on  account  of  the 
very  large  sebaceous  glands  with  their  wide  excretory  ducts,  do  not 
furnish  good  microscopic  specimens.  Small  sebaceous  glands  with  hair- 
follicles  can  be  seen  with  the  unaided  eye  in  stripping  off  the  macerated 
epidermis  of  old  cadavers. 

No.  165. — Blood-vessels  of  the  Skin. — Inject  with  Berlin  blue  the 
entire  hand  of  a  child  through  the-ulnar  artery  (or  a  foot  through  the 
posterior  tibial  artery)  and  place  it  in  from  i  to  2  liters  of  Muller's  fluid  ; 
after  several  days  cut  pieces  2  or  3  cm.  square  of  the  palm  of  the  hand 
or  of  the  sole  of  the  foot,  place  them  (two  or  four  weeks)  in  100  or 
200  c.c.  of  Muller's  fluid  and  harden  them  in  100  c.c.  of  gradually- 
strengthened  alcohol.  Cut  thick  sections  and  mount  them  unstained  in 
damar  (Fig.  249).  The  papillae  in  such  sections  can  only  be  recog- 
nized by  the  capillary  loops.  To  the  beginner  it  appears  as  if  the  loops 
extend  into  the  stratum  germinativum. 

No.  1 66. — For  a  general  view  of  the  mammary  gland  place  the 
nipple  and  a  portion  of  the  gland  (3  or  4  cm.  square)  in  60  or  100  c.c. 
of  absolute  alcohol.  If  possible,  obtain  the  glands  of  an  individual  that 
was  pregnant  not  too  long  a  time  before,  also  the  glands  of  virgins,  etc. 
Make  vertical  sections  through  the  nipple  and  in  any  direction  through 
the  gland-substance,  and  stain  them  with  Hansen's  hematoxylin  ;  mount 
in  damar  (Fig.  251). 

No.  167. — For  the  minute  structure  of  the  mammary  glands  place 
the  warm  living  tissue  (3  or  5  mm.  cubes)  of  a  pregnant  mammal  in  5 
c.c.  of  Flemming's  mixture  (p.  32),  and  harden  after  one  or  two  days  in 
30  c.c.  of  gradually-strengthened  alcohol.  Cut  very  thin  sections,  stain 
them  with  safranin  (p.  38),  and  mount  in  damar  (Fig.  250).  The  struct- 
ure is  often  difficult  to  understand  on  account  of  the  small  size  of  the 
gland-cells  (in  the  rabbit). 

No.  1 68. — Elements  of  Milk. — Put  a  drop  of  salt  solution  on  a  clean 
slide  and  add  to  it  a  drop  of  milk.  The  milk  is  to  be  obtained  by  plac- 
ing the  cover-glass  upon  the  nipple  and  then  pressing  out  a  drop.  Ex- 
amine with  a  high  power  (Fig.  252,  A). 

No.  1 68  a. — Elements  of  Colostrum. — Obtain  the  colostrum  shortly 
before  parturition.  Proceed  as  in  No.  168.  Be  careful  to  avoid  pressure 
on  cover-glass.  The  nuclei  of  the  colostrum  corpuscles  can  rarely  be 
distinctly  seen  without  further  treatment  ;  on  the  addition  of  a  drop  of 
picrocarmine  they  appear  as  dull-red  spots  (Fig.  252,  B). 


XI.  THE  EYE  AND  ITS  APPENDAGES. 

The  organ  of  vision   consists  of  the  eyeball,  the   optic  nerve,  the 
eyelids,  and  .the  lacrymal  glands. 


THE  EYEBALL. 

The  eyeball  (bulbus  oculi)  is  a  hollow  globe,  which  encloses  partly 
formed,  partly  fluid  contents.  The  walls  of  the  eyeball  are  composed  of 
three  coats  :  (i)  the  tunica  externa,  a  fibrous  membrane  in  which  an 
anterior  transparent  division,  the  cornea,  may  be  distinguished  from  the 
remaining  opaque  portion,  the  sclera  ;  (2)  the  tunica  media,  rich  in  blood- 
vessels, which  includes  three  divisions,  the  cJwroid,  the  ciliary  body,  and 
the  iris  ;  (3)  the  tunica  interna,  the  retina,  which  contains  the  specialized 
terminal  apparatus  of  the  optic  nerve.  The  formed  contents  within  the 
eyeball  are  the  lens  and  the  vitreous  body. 

THE   TUNICA    EXTERNA. 

The  cornea  consists  of  five  strata,  which  enumerated  from  before 
backward  are  the  following  : — 

1.  The  corneal  epithelium. 

2.  The  anterior  elastic  lamina. 

3.  The  substance  proper. 

4.  The  posterior  elastic  lamina. 

5.  The  corneal  "endothelium." 

The  corneal  epithelium  is  a  stratified  scaly  epithelium  and  consists  of 
a  lowermost  layer  of  sharply-contoured  columnar  cells,  which  is  followed 
by  three  or  four  (more  in  animals)  layers  of  spherical  cells,  that  in  turn 
are  covered  by  several  strata  of  flattened  elements  still  possessing  nuclei. 
The  thickness  of  the  epithelium  in  man  is  0.03  mm.  At  the  rim  of  the 
cornea  the  epithelium  is  continuous  with  that  of  the  conjunctival  sclera. 

The  anterior  elastic  lamina  (Bowman's  membrane,  anterior  basal 
membrane)  in  man  is  a  distinctly-visible  stratum,  about  o.oi  mm.  thick, 
and  almost  homogeneous  in  appearance.  The  surface  is  provided  with 
minute  serrations  and  ridges  for  the  attachment  of  the  columnar  cells  of 

341 


342 


HISTOLOGY. 


the  corneal   epithelium.      Posteriorly  it  gradually   passes   into  the  sub- 
tantia  propria  of  the  cornea,  of  which  it  is  a  special  modification. 

The  substance  proper  (substantia  propria  corneae)  constitutes  the  chief 
bulk  of  the  cornea.  It  consists  of  delicate  parallel  fibrillae,  which  are 
united  by  an  interfibrillar  cement-substance  into  bundles  of  nearly 
uniform  thickness  ;  the  bundles  in  turn  are  united  by  an  interfascicular 
cement-substance  into  flat  lamellae,  which  lie  in  many  superposed  strata 
and  are  held  together  by  an  interlamellar  cement-substance.  The 
lamellae  are  arranged  parallel  to  the  surface  of  the  cornea  and  run  in 


Corneal  epithelium. 

Lamina  elastica  ante- 
rior. 


^»«i*iiigi|S_ 


Substantia  propria... 


Lamina  elastica  poste- 
rior. 

Corneal  endothelium. 

FIG.  253. — VERTICAL  SECTION  OF  A  HUMAN  CORNEA.    X  ico.    Techn.  No.  169  b. 

meridional  curves  one  above  the  other,  so  that  a  vertical  section  through 
the  center  of  the  cornea  shows  alternate  longitudinal  and  transverse 
bundles.  A  number  of  bundles  running  obliquely,  the  so-called  arcuate 
fibers,  unite  each  lamella  with  its  neighbor  above  or  below ;  especially 
well-developed  arcuate  fibers  occur  in  the  anterior  strata  of  the  substantia 
propria. 

Embedded  in  the  cement-substance  is  an  intercommunicating  sys- 
tem of  much-branched  canaliculi,  the  corneal  canaliculi,  lymph-canaliculi, 
which  at  many  places  are  expanded  to  broad  oval  lacunae,  the  corneal 


THE    EYE    AND    ITS    APPENDAGES. 


343 


spaces,  lymph-spaces  (Fig.  254).  The  latter  lie  between  the  lamellae, 
while  the  canaliculi  also  penetrate  between  the  bundles.  The  lacunae 
and  canaliculi  contain  a  serous  fluid  and  cells,  "  fixed  "  corneal  corpuscles 


. 


Corneal  canaiiculi.           Corneal  spaces.  Corneal  corpuscles. 

FIG.  254. — HORIZONTAL  SECTION  OF  THE  CORNEA  FIG.  255. — HORIZONTAL  SECTION  OF  THE  CORNEA 

OF  AN  Ox.    Silver-preparation  ;  negative  picture  ;  OF  A  RABBIT.      Positive  picture  of  the  corneal 

the    canalicular   system    is    light    upon  a  dark  canaliculi.     X  about  240.     Techn.  No.  174. 
ground.     X  about  240.    Techn.  No.  173. 

and  wandering  cells.  The  corneal  corpuscles  are  flattened  connective- 
tissue  cells  possessing  large  nuclei  (Fig.  255)  ;  they  lie  against  one  wall 
of  the  lacunae. 


Cross-  and  longitudinal- 
sections  of  bundles  of 
scleral  fibers. 

Lamina  suprachoroidea. 


Lamina  vasculosa. 


Boundary1  zone. 

_ —  Choriocapillaris. 
~   Basal  membrane. 

Pigment  layer  of  the  retina. 

FIG.  256.— VERTICAL  SECTION.  THROUGH  A  PART  OF  THE  HUMAN  SCLERA  AND  THE  ENTIRE  CHOROID. 
X  loo.    g.  Larger  vessels;  /,  pigment  cells  ;  c,  cross-sections  of  capillaries.     Techn.  No.  169  c. 

The  posterior  elastic  lamina  (membrane  of  Descemet,  posterior  basal 
membrane)  is   a  transparent   elastic   layer,  only   0.006  mm.    thick.      In 


344  HISTOLOGY. 

adult  man  the  posterior  surface,  at  the  periphery  of  the  cornea,  is  beset 
with  hemispherical  protuberances. 

The  corneal  endothelium  is  composed  of  a  single  layer  of  flat,  polyg- 
onal cells,  with  often  slightly-projecting  nuclei. 

The  sclera  principally  consists  of  interlacing  bundles  of  connective 
tissue,  extending  for  the  most  part  in  meridional  and  equatorial  direc- 
tions. In  addition,  delicate  elastic  fibers  arranged  in  networks  and  flat- 
tened connective-tissue  cells  are  present ;  the  latter,  like  the  corneal 
corpuscles,  lie  in  lacunae,  that  differ  from  the  corneal  spaces  only  in 
having  more  irregular  outlines.  Between  the  sclera  and  the  choroid  is  a 
layer  of  loose,  highly-elastic  tissue  containing  branched  pigmented  cells 
and  flattened  elements  free  from  pigment  ("  endothelial  "  cells),  which  on 
separating  the  two  coats  adheres  partly  to  the  former  and  partly  to  the 
latter  ;  the  portion  on  the  sclera  is  called  the  lamina  fuse  a  scler<zy  that  on 
the  choroid,  lamina  suprachoroidea. 

The  sclera  is  thickest  posteriorly  (one  millimeter),  and  becomes 
gradually  thinner  toward  the  cornea. 

THE   TUNICA    MEDIA. 

The  clwroid  is  characterized  by  the  great  abundance  of  its  blood- 
vessels,which  are  arranged  in  two  layers.  The  superficial  layer,  adjoining 
the  inner  side  of  the  lamina  suprachoroidea,  the  lamina  vasculosa  (layer  of 


FIG.  257. — A.  FROM  A  TEASED  PREPARATION  OF  A  HUMAN  CHOROID.     X  240.    p.  Pigment  cells;  e,  elastic 

fibers;  k,  nucleus  of  a  flat  nonpigmented  cell ;  the  cell-body  is  invisible. 
B.  PORTION  OF  HUMAN  CHORIOCAPILLARIS  AND  THE  ADHERENT  HYALOID  MEMBRANE.     X  240.    c.  Wide 

capillaries,   some  of  which   contain    (b)   blood-corpuscles;    <?,    hyaline   membrane,   snowing  a   fine 

"lattice-work."     Techn.  No.  170  a. 

large  blood-vessels),  contains  the  ramifications  of  the  arterial  and  venous 
channels,  that  are  embedded  in  a  supporting  tissue,  the  stroma,  consist- 
ing of  networks  of  fine  elastic  fibers  and  numerous  branched  pigment- 
cells.  In  addition,  the  stroma  contains  the  tissues  accompanying  the 


THE    EYE    AND    ITS    APPENDAGES. 


345 


large  arteries  ;  namely,  fibrillar  connective  tissue,  smooth  muscle-fibers, 
and  nonpigmented  plate-like  cells  that  are  united  in  delicate  "  endothe- 
lial  "  membranes.  The  deeper  layer,  the  lamina  clwriocapillaris,  or  layer 
of  capillary  networks,  is  composed  of  a  narrow-meshed  net  of  capillaries, 
between  which  no  formed  elements  are  found.  Between  the  two  lamina: 
of  blood-vessels  lies  the  boundary  zone,  a  portion  of  the  stroma  consisting 
of  networks  of  fine  elastic  fibers  and  almost  devoid  of  pigment.  In 
ruminants  and  horses  this  zone  consists  of  wavy  bundles  of  connective 
tissue,  to  which  is  due  the  metallic  reflex  seen  in  the  eyes  of  these 
animals.  This  shining  membrane  is  known  as  the  tapetum  fibrosum. 
The  similar  iridescent  tapetum  cellulosum  of  carnivora  is  composed  of 
several  strata  of  plate-like  cells  containing  numerous  minute  crystals. 


FIG.  258.— MERIDIONAL  SECTION  THROUGH  THE  RIGHT  IRIDO-CORNEAL  ANGLE  OF  MAN.  X  30.  i.  Epi- 
thelium, 2,  connective  tissue  of  the  conjunctiva.  3,  Sclera.  4,  5,  6,  7,  and  8.  Ciliary  body  ;  4,  meridi- 
onal, 5,  radial,  6,  circular  fibers  of  ciliary  muscle;  7,  ciliary  process;  8,  ciliary  portion  of  retina. 
9.  Iridal  portion  of  retina.  10.  Stroma  of  the  iris,  n,  12,  and  13.  Cornea;  n,  posterior  elastic  lamina  ; 
12,  substantia  propria;  13,  epithelium.  14.  Venous  sinus  of  sclera.  13.  Angle  of  iris.  Techn.  No. 
169  a. 

Attached  to  the  lamina  choriocapillaris  is  the  lamina  basalts  or 
vitreous  lamina,  a  structureless  lamella  about  2  <j.  thick,  which  on  its 
outer  surface  is  provided  with  delicate  lattice-like  markings.  The 
polygonal  areas  noticeable  on  its  inner  surface  are  imprints  of  retinal 
pigment.  The  vitreous  membrane  approaches  in  character  the  elastic 
membranes. 

The  ciliary  body  is  formed  by  the  ciliary  processes  and  the  muscular 
ring  lying  upon  them,  the  ciliary  muscle.  The  ciliary  processes  are  seventy 
or  eighty  meridionally-placed  folds,  which  begin  low  at  the  ora  serrata, 
gradually  attain  a  height  of  one  millimeter,  and  terminate  with  an  abrupt 
descent  near  the  edge  of  the  lens.  Kach  ciliary  process  consists  of  fibrillar 
connective  tissue  containing  numerous  blood-vessels  and  inwards  is  limited 


HISTOLOGY. 


by  a  continuation  of  the  vitreous  membrane,  that  here  is  distinguished  by 
minute  intersecting  folds.  The  blood-vessels  of  the  ciliary  processes 
supply  the  intraocular  fluid.  The  ciliary  muscle  is  an  annular  band  about 
3  mm.  broad,  anteriorly  0.8  mm.  thick,  arising  from  the  inner  wall  of  the 
venous  sinus  of  the  sclera.  The  nonstriped  elements  of  which  it  is  com- 
posed extend  in  three  different  directions.  We  distinguish  (a)  meridional 
fibers  (Fig.  258,  4),  numerous  fasciculi  lying  next  to  the  sclera,  which  reach 
to  the  smooth  portion  of  the  choroid  and  are  known  as  the  tensor  cho- 
roideae  ;  (ft)  radial  fibers,  lying  next  to  the  meridional  bundles,  which  from 
without  inward  progressively  assume  a  more  radial  disposition  (oriented 
to  the  center  of  the  bulbus  oculi)  and  posteriorly,  still  in  the  region  of 
the  ciliary  body,  turn  and  follow  a  circular  course  (5)  ;  (c)  circular 
(equatorial)  fibers,  the  so-called  ring-muscle  of  Muller  (6). 

Trie  iris  consists  of  a  stroma  divided  in  three  layers,  covered  anteriorly 


i.  Endothelial  nuclei. 


2:  Anterior  boundary 
layer. 


3.  Vascular  layer. 


4.  Posterior    boundary 
layer. 


5.  Pigment  layer. 

F 

FIG.  259. — VERTICAL  SECTION  OF  THE  PUPILLARY  PORTION  OF  A  HUMAN  IRIS.  X  100.  About  one-fifth 
of  the  entire  width  of  the  iris  is  shown,  g.  Blood-vessel,  with  thick  connective-tissue  sheath ;  m, 
sphincter  pupillae  muscle  cut  transversely  ;  /,  pupillary  border  of  the  iris.  Techn.  No.  170  c. 

by  a  continuation  of  the  posterior  endothelium  of  the  cornea  and  pos- 
teriorly by  a  modified  extension  of  the  retina.  Accordingly  five  layers 
may  be  distinguished  : — 

1.  The  anterior  "  endothelium." 

2.  The  anterior  boundary  layer. 

3.  The  vascular  layer. 

4.  The  posterior  boundary  layer. 

5.  The  pigment  layer. 

The  anterior  endothelium  covers  the  anterior  surface"  of  the  iris  and, 
like  that  on  the  posterior  surface  of  the  cornea,  consists  of  a  single  layer 
of  flattened  polygonal  cells. 

The  anterior  boundary  layer  (reticular  layer)  comprises  three  or  four 


THE    EYE    AND    ITS    APPENDAGES.  347 

strata  of  networks,  which  are  formed  by  stellate  connective-tissue  cells  ; 
it  resembles  the  reticulum  of  adenoid  tissue.  The  posterior  stratum 
gradually  passes  into  the  adjoining  vascular  stroma. 

The  vascular  layer  of  the  iris  contains  numerous  radially-disposed 
(to  the  pupil)  blood-vessels  embedded  in  a  stroma  consisting  of  slender, 
loosely-united  bundles  of  connective  tissue.  The  blood-vessels  and 
nerves  are  provided  with  conspicuously  thick  connective-tissue  sheaths. 
There  are  smooth  muscle-fibers  in  the  vascular  stroma,  arranged  in  two 
sets,  (i)  as  annular  bundles  encircling  the  pupillary  margin  of  the  iris  in  a 
zone  about  one  millimeter  in  width,  constituting  the  sphincter  of  the  pupil, 
and  (2)  as  a  few  radially-disposed  bundles,  which  do  not  form  a  contin- 
uous layer,  the  dilator  of  the  pupil.  In  the  anterior  boundary  layer  and 
in  the  vascular  stroma  pigmented  cells  occur  in  greatly  varying  num- 
bers ;  in  blue  eyes  they  are  absent. 

The  posterior  boundary  layer  is  a  clear,  glassy,  homogeneous  mem- 
brane, elastic  in  its  nature. 

The  pigment  layer  of  the  iris  (pars  iridica  retinae)  comprises  two 
layers,  of  which  the  anterior  contains  spindle-shaped,  the  posterior 
polygonal  pigment-cells.  Both  layers  are  so  crowded  with  pigment- 
granules  that  recognition  of  the  individual  elements  is  almost  impossible. 
The  pigment  is  wanting  only  in  albinos.  The  posterior  surface  of  the 
pigment  layer  is  covered  by  an  exceedingly  delicate  membrane,  the  mem- 
brana  limitans  iridis,  a  continuation  of  the  membrana  limitans  interna 
retinae. 

The  Irido-corneal  Angle. — The  junction  of  the  sclera  and  the 
cornea  is  of  especial  interest,  since  here  the  iris,  the  cornea,  and  the 
ciliary  body  meet.  The  transition  of  the  sclera  into  the  cornea  is  abso- 
lutely direct ;  the  more  wavy  bundles  of  the  sclera  without  interruption 
in  continuity  pass  over  into  the  straight  bundles  of  the  cornea,  the  sys- 
tem of  canaliculi  of  the  sclera  communicates  with  that  of  the  cornea. 
The  line  of  transition  is  oblique  and  microscopically  not  sharply  defined, 
because  the  transformation  of  the  sclera  into  the  tissues  of  the  cornea 
takes  place  sooner  in  the  posterior  than  in  the  anterior  strata  of  the 
tunica  externa.  At  the  periphery  of  the  cornea  the  posterior  elastic 
lamina  and  the  hindermost  laminae  of  the  substance  proper  meet  the 
ciliary  border  of  the  iris  and  form  the  irido-corneal  angle  (Fig.  258,  15). 
Here  the  iris  sends  toward  the  posterior  surface  of  the  posterior  elastic 
lamina  connective-tissue  processes,  the  iridal  processes,  that,  well  devel- 
oped in  animals  (cattle,  horses),  constitute  the  so-called  ligamentum  iridis 
pectinatuui.  In  man  these  processes  are  inconspicuous.  At  the  per- 
iphery of  the  cornea  the  posterior  elastic  lamina  splits  into  fibers  which, 


348 


HISTOLOGY. 


strengthened  by  contributions  from  the  intramuscular  connective  tissue 
of  the  ciliary  muscle  and  from  the  elastic  tendons,  also  with  accessions 
in  a  lesser  degree  from  the  sclera,  blend  with  the  iridal  processes.  The 
tissues  participating  in  the  formation  of  the  loose  mass  of  fibers  occupy- 
ing the  angle  of  the  iris  are  derived  from  the  structures  that  meet  one 
another  at  the  irido-corneal  angle  :  cornea,  sclera,  iris,  and  ciliary  muscle. 
The  posterior  endothelium  of  the  cornea  continued  on  to  the  surface  of 
the  iris  forms  a  sheath  for  these  fibers.  The  spaces  between  them,  that 
stand  in  open  connection  with  the  anterior  chamber  of  the  eye  and  con- 
tain the  same  fluid,  are  called  the  spaces  of  Fontana.  In  man  they  are 
scarcely  developed. 

THE   TUNICA    INTERNA. 

The  retina  extends  from  the  entrance  of  the  optic  nerve  to  the 
pupillary  margin  of  the  iris  and  in  this  tract  three  zones  may  be  distin- 
guished :  (i)  the  pars  optic  a  retin<z,  the  entire  expanse  of  the  optic  nerve  ; 


i.  Pigment    layer 
(not  shown). 


—  2.  Layer  of  rods 
and  cones. 


Capillary. 


Pyramidal  expansion  of  a  radial-fiber. 


—  3.  Membranalim- 
itans  externa. 


4.  Outer  granule 
layer. 


—  5.  Fiber-layer   of 

Henle. 

—  6.  Outer  reticular    i 

layer. 

—  7.  Inner    granule 

layer. 


—  8.  Inner  reticular 
layer. 


—  9.  Ganglion-cell 

layer. 

—  10.  Nerve-fiber 

layer. 


Neuro- 

epithelial 

layer. 


Cerebral 
layer. 


FIG.  260.— VERTICAL  SECTION  OF  A  HUMAN  RETINA,  FROM  THE  POSTERIOR  PORTION  OF  THE  EYEBALL. 

X  400.— (After  Schaper.) 


(2)  the  pars  ciliaris  retince,  extending  from  the  ora  serrata  to  the  ciliary 
margin  of  the  iris  ;  (3)  the  pars  iridica  retincz,  which  covers  the  posterior 
surface  of  the  iris  from  the  ciliary  to  the  pupillary  margin. 

The  pars  optica  retince,  the  portion   of  the  retina  alone  sensitive  to 
light,  lines  the  entire  posterior  segment  of  the  eyeball  and  extends  to 


THE    EYE    AND    ITS    APPENDAGES. 


349 


within  a  short  distance  of  the  ciliary  body,  where  it  terminates  in  a  sharp, 
macroscopically  perceptible,  serrated  line,  the  ora  scrrata.  It  falls  into 
t\vo  divisions,  an  outer  neuro- epithelial  lamina,  and  inner  cerebral  lamina. 
In  each  of  these  divisions  several  layers  may  be  distinguished,  four  in  the 
neuro-epithelial  lamina,  five  in  the  cerebral  lamina ;  if  the  pigment  layer 
(pigment-epithelium)  lying  close  beneath  the  choroid,  that  genetically 
belongs  to  the  retina,  is  added,  there  are  ten  layers,  that  from  without 
inward  are  arranged  in  the  following  order  : — 
i.  The  pigment  layer. 

The  layer  of  rods  and  cones.          -\ 

The  membrana  limitans  externa.     >  Neuro-epithelial  layer. 


The  outer  granule  layer. 
The  fiber-layer  of  Henle. 

6.  The  outer  reticular  layer. 

7.  The  inner  granule  layer. 

8.  The  inner  reticular  layer. 

9.  The  ganglion-cell  layer. 
10.   The  nerve-fiber  layer.* 


J 


Cerebral  layer. 


The  elements  of  the  preceding  layers  are  only  in  part  nervous  or 
epithelial  in  their  nature  ;  the  other  part  is  formed  of  supporting  sub- 
stance, that  however  is  not  of  the  nature  of  connective  tissue  (p.  169). 
The  most  conspicuous  elements  of  the  supporting  tissue  are  the  radial 
fibers  (Mutter),  elongated  cells  which  extend  from  the  inner  surface  of 
the  retina  through  all  the  layers  to 
the  rods  and  cones.  The  inner  end 
of  the  fibers  is  characterized  by  a 
conical  foot,  the  radial-fiber  pyra- 
mid ;  the  expanded  bases  of  these 
pyramids  are  so  closely  placed 
beside  one  another  that  they  ap- 
parently produce  a  continuous 
membrane  on  the  inner  surface  of 
the  retina,  the  so-called  membrana 
limitans  interna.  From  the  apex 
of  the  pyramids  the  radial  fibers, 
with  progressive  decrease  in  thick- 

ness, proceed  through  the   inner   reticular   layer  to  the   inner  granule 
layer,  where   they  are  provided  with   a   nucleus  ;   from   here  they  pass 


Pigment  epithelium.  - 

Rods  and  cones.  ! 

External  limiting  membrane.   -£ 

Outer  granule  layer. 

Outer  reticular  layer.  { 

Inner  granule  layer. 


Inner  reticular  layer. 

Ganglion-cell  layer    1. 
Nerve-fiber  layer.   — 


FIG.  261.— VERTICAL  SKCTION  OK  THE  RETINA  OF 
A  RABBIT.  X  240.  k.  Expanded  base  of  radinl 
fibers ;  n,  nucleated  portion  of  the  same  ;  /, 
"  membrana  limitans  interna."  Techn.  No.  170  d. 


*  To  these  the  membrana  limitans  interna  is  sometimes  added  as  an  eleventh  layer,  but 
it  does  not  represent  an  independent  membrane. 


35°  HISTOLOGY. 

through  the  outer  reticular  and  outer  granule  layer  to  the  external 
limiting  membrane,  with  which  they  unite.  Throughout  their  entire 
course  the  radial  fibers  give  off  lateral  processes  for  the  support  of  the 
nervous  elements.  In  addition  to  these  radial  supporting  cells,  concentric 
supporting  cells  are  found  in  the  outer  reticular  layer ;  they  extend 
parallel  to  •  the  surface,  are  provided  with  long  processes,  are  partly 
nucleated,  partly  nonnucleated.  Glia-cells  occur  in  the  vicinity  of  the 
optic  entrance.  From  the  surface  of  the  membrana  limitans  externa 
delicate  processes  extend  to  the  rods  and  cones,  the  bases  of  which  they 
embrace  as  the  so-called  fiber-crates  (Fig.  262).  A  portion  of  both  the 
reticular  layers  belongs  to  the  supporting  substance,  as  also  the  small 
quantity  of  cement-substance  in  the  ganglion-cell  layer. 

In  the  more  detailed  description  of  the  individual  layers  of  the 
retina  the  series  will  be  taken  up  in  the  reverse  order,  from  within  out- 
ward. 

THE  CEREBRAL  LAYER. 

The  nerve-fiber  layer  consists  of  naked  axis-cylinders  which, 
arranged  in  bundles,  are  united  in  a  sort  of  plexus.  From  the  entrance 
of  the  optic  nerve,  where  the  fiber-layer  is  thickest,  the  fibers  expand  in  a 
radial  direction  to  the  ora  serrata.  The  radial  arrangement  of  the  fibers 
is  disturbed  in  the  region  of  the  macula  lutea.  The  majority  of  the  axis- 
cylinders  are  centripetal  fibers,  which  originate  in  the  ganglion-cells  of 
the  retina  ;  the  smaller  portion  are  the  axis-cylinder  processes  of  cerebral 
ganglion-cells,  centrifugal  fibers,  which  ramify  in  the  inner  granule  layer 
and  terminate  in  free  endings. 

The  ganglion-cell  layer  ("  ganglion  nervi  optici  ")  consists  of  a  single 
row  of  large  multipolar  ganglion-cells,*  which  send  one  unbranched  axis- 
cylinder  process  (nerve-process)  centralward,  toward  the  nerve-fiber 
layer,  one  or  more  branched  protoplasmic  processes  (dendrites)  periph- 
eryward,  toward  the  inner  reticular  layer ;  there  they  divide  and  are 
arranged  in  delicate  networks  lying  parallel  to  the  surface,  which  with 
the  processes  from  other  ganglion-cells  form  a  dense  nervous  tangle 
(Fig.  262). 

The  inner  reticular  layer  ("  neurospongium  ")  consists  of  an  exceed- 
ingly delicate  network  of  supporting  tissue,  which  sustains  a  dense  fiber- 
maze  in  the  formation  of  which  processes  of  all  the  ganglion-cells  of  the 
retina  participate. 

The  inner  granule  layer  includes  elements  that  differ  greatly  in  their 

*  A  few  of  these  cells  are  marked  by  their  large  size  ;  such  giant-ganglion-cells  occur  at 
tolerably  regular  intervals. 


THE    EYE    AND    ITS    APPENDAGES. 


351 


nature.  The  innermost  stratum  consists  of  large  ganglion-cells,*  which 
send  branched  processes  into  the  inner  reticular  layer.  From  many  of 
these  cells — but  not  all — a  nerve-process  passes  to  the  optic-fiber  layer 
(Fig.  262).  The  remaining  strata,  for  the  greater  part,  are  composed  of 
small  bipolar  ganglion-cells  (ganglion  retinae),  the  central  process  of 
which  extends  into  the  inner  reticular  layer  and  there  breaks  up  into 
delicate  varicose  branches,  while  the  peripheral  process  passes  to  the 
outer  reticular  layer ;  there  it  divides  into  forks,  spreads  out  parallel  to 
the  surface  and  resolves  into  extremely  minute  fibrillae  which  pass  into 


Fiber-crate. 


Concentric 
sustentac- 
ular  cell 
(nucleated).    '- 


Concentric 
sustentac- 
ular  cell 
(nonnucle- 
ated). 

Radial-fiber. 


Conical  base 
of  radial- 
fiber. 


Limiting 
mem- 
brane. 


Rods  and 
cones. 


Nuclei  of 
rods  and 
cones. 


Outer       Subepithe- 
reticular        lial  gang- 
layer,  lion-cell. 


Stellate 
ganglion- 
cell. 

Bipolar 
ganglion- 
cell. 

Multipolar 
ganglion- 
cell. 


Inner  re- 
ticular 
layer. 


Centrifugal 
nerve -fiber. 


Multipolar 
ganglion- 
cell. 

Nerve-fiber 
layer. 


FIG.  262.— SCHEME  OF  THE   ELEMENTS  OF   THE   RETINA  ;   the  figure  on  the  left  represents  the  sup- 
porting elements,  that  on  the   right  the  nervous  and  epithelial  elements. 

a  subepithelial  tangle  formed  by  the  felting  of  processes  of  neighboring 
ganglion-cells.  All  bipolar  ganglion-cells  send  up  one  process  between 
the  visual  cells,  that  near  the  membrana  limitans  terminates  in  a  minute 
knob  (Fig.  262).  Finally,  the  nuclei  of  the  radial  fibers  occur  in  this 
layer. 

At   the   border  of  this  zone,  next   to   the  outer  reticular  layer,  lie 

*  These  cells  were  formerly  called  spongioblasts,  because  they  were  erroneously  regarded  as 
the  producers  of  the  "  neurospongium  ";  they  are  elements  of  the  ganglion  of  the  optic  nerve 
which,  unlike  the  other  elements,  have  not  wandered  through  the  inner  reticular  layer. 


352  HISTOLOGY. 

small  and  large  stellate  cells  ;  they  send  many  processes  to  participate 
in  the  formation  of  the  subepithelial  network  ;  one  process  runs  to  the 
inner  reticular  layer,  where  it  terminates  in  minute  branches,  and  another 
— the  nerve-process — after  a  long  horizontal  course,  bends  and  passes 
in  a  vertical  direction  to  the  nerve-fiber  layer.* 

The  outer  reticular  layer  (subepithelial  layer)  likewise  is  a  delicate 
network  of  sustentacular  tissue,  which  supports  the  nervous  tangle  just 
described.  The  cellular  elements  of  this  layer  include  the  concentric 
sustentacular  cells  and  the  "  subepithelial  ganglion-cells  "  ;  the  latter  are 
dislocated  elements  of  the  ganglion  retinae,  that  differ  from  the  bipolar 
ganglion-cells  only  in  their  rounded  form,  entirely  agreeing  with  the 
latter  in  regard  to  their  terminal  ramifications  (Fig.  262). 

THE  NEURO-EPITHELIAL  LAYER. 

The  neuro-epithelial  layer  consists  of  two  kinds  of  elements,  the 
rod-visual  cells  and  the  cone-visual  cells,  that  are  characterized  by 
the  situation  of  the  nucleus  in  the  lower  half  of  the  cell  and  the  sharp 
demarcation  of  the  upper  nonnucleated  division  from  the  lower  portion 
by  the  perforated  membrana  limitans  externa.  This  gives  rise  to  the 
appearance  of  different  layers,  the  inner  nucleated  portion  of  the  visual- 
cells  being  known  as  the  outer  granule  layer,  the  outer  nonnucleated 
division  as  the  layer  of  rods  and  cones.  Between  these  two  lies  the 
limiting  membrane. 

The  Rod-visual  Cells. — The  outer  halves  of  these  elements  are  the 
rods,  slender  cylinders  (60  /JL  long,  2  /JL  thick),  which  consist  of  a  homo- 
geneous outer  segment  and  a  finely-granular  inner  segment.  The  outer 
segment  is  the  exclusive  seat  of  the  visual  purple.  The  inner  segment 
possesses  in  its  outer  end  an  ellipsoidal,  fibrillated  body,  the  fiber-body. 
The  inner  halves  of  the  rod-visual  cells  are  named  rod-fibers  ;  they  are 
exceedingly  delicate  filaments  which  are  provided  with  nucleated  expan- 
sions, the  rod-granules.  The  nuclei  are  marked  by  from  one  to  three 
clear  transverse  bands.  The  basal  end  of  the  cell  is  prolonged  as  a 
minute  process  terminating  in  a  free,  club-shaped  expansion  (Fig.  262). 

The  Cone-visual  Cells. — The  outer  halves  of  these  cells,  the  cones, 
likewise  consist  of  an  outer  segment  and  an  inner  segment.  The  outer 
segments  are  conical  and  shorter  than  those  of  the  rods.  The  inner 
segments  are  thick  and  expanded  ;  therefore  the  cone  as  a  whole  is  flask- 
shaped.  The  inner  segment  of  the  cones  also  contains  a  fiber-body. 


*  According  to  other  authors  this  process  ends  in  the  outer  reticular  layer,  where  its  ramifi- 
cations surround  the  base  of  the  visual  cells. 


THE    EYE    AND    ITS    APPENDAGES. 


353 


The  inner  halves  of  the  cone-visual  cells  are  the  cone-fibers  ;  these  are 
broad  and  rest  with  an  expanded  pyramidal  foot  on  the  outer  reticular 
layer.  The  nucleated  enlargement,  the  cone-granule,  usually  lies  imme- 
diately to  the  inner  side  of  the  membrana  limitans. 

The  number  of  the  rods  is  much  greater  than  that  of  the  cones. 
The  latter  occur  at  regular  intervals,  so  that  three  or  four  rods  always  lie 
between  two  cones  (Fig.  260). 

The  basal  portions  of  the  visual  cells  resting  upon  the  outer  reticular 
layer  usually  are  plainly  to  be  recognized  as  a  special  radially-striated 
layer  (Fig.  260),  Henle's  fiber-layer ;  in  the  region  of  the  macula  lutea 
this  fiber-layer  is  particularly  broad  and  gradually  diminishes — often  very 
unsymmetrically — toward  the  ora  serrata. 


-O 


FIG.  263. — ISOLATED  ELEMENTS  OF  THE  RETINA  OF  AN  APE.  X  240.  i.  Mutilated  ganglion-cell  of  the 
ganglion  of  the  optic  nerve.  2.  Elements  of  the  inner  granule  layer.  3.  Rod-visual  cells  and  frag- 
ments of  the  same  ;  below,  two  outer  segments,  one  of  which  exhibits  transverse  striation,  the  begin- 
ning of  a  disintegration  into  transverse  platelets;  above  are  two  rods,  the  outer  segment  of  the  lower 
one  falling  apart.  The  uppermost  figure  shows  more  complete  rod-cells;  a,  outer  segment;  i,  inner 
segment;  k,  nucleus  of  rod  ;  ,r,  fiber-body.  4.  Cone-visual  cells  :  a,  outer  segment ;  i,  inner  segment ; 
k,  nucleus  of  cone  ;  /",  cone-fiber, .torn  at  lower  end  ;  x,  fiber-body.  5.  Radial-fiber,  £,  nucleus  of  the 
same;  r,  pyramidal  base  of  radial-fiber.  Techn.  No.  172. 

The  pigmented  epithelium  consists  of  a  simple  layer  of  hexagonal 
cells,  which  on  their  outer  surface,  toward  the  choroid,  where  the  nucleus 
lies  are  free  from  pigment,  while  their  inner  division  contains  numerous 
rod-shaped  pigment-granules,  from  I  to  5  />-  long.  From  the  inner  divi- 
sion numerous  delicate  processes  extend  between  the  rods  and  cones.  In 
albinos  and  on  the  tapetum  the  epithelium  is  free  from  pigment. 

In  the  region  of  the  macula  lutea  and  fovea  centralis,  also  of  the  ora 
serrata,  the  structure  of  the  retina  above  described  presents  modifications 
calling  for  special  consideration. 

Macula  Lutea  and  Fovea  Centralis. — In  the  region  of  the  macula  the 
layers  of  the  retina  exhibit  the  following  variations.  Delicate  fibers  of 
the  optic  nerve  run  direct  from  the  optic  entrance  to  the  adjacent  median 
portion  of  the  macula  ;  above  and  below  these  fibers,  thicker  nerve-fibers 
run  from  the  optic  entrance  convexly  upward  and  downward  and  unite 
at  the  lateral  margin  of  the  macula.  The  ganglion-cell  layer  is  greatly 
23 


354 


HISTOLOGY. 


THE    EYE    AND    ITS    APPENDAGES.  355 

increased  in  thickness,  owing  to  the  development  of  the  layer  of  bipolar 
ganglion-cells,  which  instead  of  a  single  row  are  arranged  in  many  (up 
to  nine)  rows  ;  also  the  inner  granule  layer  by  multiplication  of  its  ele- 
ments is  almost  twice  as  broad.  The  inner  and  outer  reticular  layers 
suffer  no  essential  change.  The  neuro-epithelial  layer  is  here  repre- 
sented by  the  somewhat  smaller  cone-visual  cells  alone.  Already  at  the 
margin  of  the  macula  the  rod-visual  cells  diminish  in  number  and  within 
the  macula  they  are  wanting  altogether  ;  as  a  result  the  cone-fibers  are 
visible  in  a  wide  extent ;  here  they  alone  form  the  fiber-layer  of  Henle. 
The  cone-granules,  on  account  of  their  large  number,  lie  in  several  rows 
one  above  the  other.  The  radial-fibers  no  longer  stand  vertically  to  the 
thickness  of  the  retina,  but  obliquely  toward  the  fovea. 

Toward  \hzfovea  centralis  situated  in  the  center  of  the  macula  the 
layers  of  the  retina  become  gradually  thinner  and  are  in  part  totally  sus- 
pended. With  the  exception  of  a  few  fibers,  the  nerve -fiber  layer  first 
disappears  ;  then  the  cerebral  layers  fuse  with  one  another  and  in  the 
center  of  the  fovea  with  the  cone-granules,  forming  a  thin  layer  in  which 
the  boundaries  of  the  individual  strata  can  no  longer  be  recognized.  In 
the  center  of  the  fovea  (fundus  fovese)  the  neuro-epithelial  layer  (cone- 
cells)  almost  alone  is  present. 

A  diffuse  yellow  pigment  permeates  the  cerebral  layer,  but  is  absent 
in  the  neuro-epithelial  layer  ;  therefore  the  fundus  foveae  is  colorless. 

In  the  region  of  the  or  a  serrata  a  rapid  diminution  in  the  retinal 
layers  takes  place.  Optic-fibers  and  ganglion-cells  disappear  before 
reaching  the  ora  serrata.  Of  the  visual  cells  the  rod-visual  cells  are  the 
first  to  vanish  ;  the  cone-visual  cells  are  still  preserved,  but  appear  to  be 
deprived  of  their  outer  segment.  Then  the  outer  reticular  layer  is  lost, 
so  that  the  outer  and  inner  granular  layers  become  confluent,  and  finally 
the  inner  reticular  layer  ceases.  The  radial  fibers  of  Miiller,  on  the  con- 
trary, persist  and  are  highly  developed.  [Within  the  region  of  the  ora 
serrata  commonly  smaller  or  larger  clefts  or  even  rather  voluminous 
spaces  occur,  which  are  called  vacuoles  (Fig.  265).  They  are  either 
confined  to  the  neuro-epithelial  layer  or  may  extend  centrally  into  the 
inner  reticular  layer.  They  are  probably  filled  with  a  lymphatic  fluid. 
The  meaning  of  these  spaces  is  unknown,  but  they  are  certainly  not  to 
be  regarded  as  pathological  or  senile  changes,  because  they  are  rather 
common  in  the  perfectly-normal  retinae  of  young  individuals. — EDITOR.] 

The  pars  ciliaris  retina  consists  of  a  simple  layer  of  slender  colum- 
nar cells,  which  gradually  originate  in  the  blended  inner  and  outer 
granule  layers  (Fig.  265).  These  cells  are  covered  on  their  centrally- 
directed  surface  by  a  cuticular  membrane,  a  true  membrana  limitans 


"8-E 


3  3  « 


"  Vacuole. 


Radial-fibers  of  Muller. 


* 


Pars  ciliaris  retinae. 


^-~.      1 

FIG.  265.— MERIDIONAL  SECTION  OF  THE  ORA  SERRATA  AND  THE  ADJACENT  PORTION  OF  THE  PARS 
CILIARIS  RETIN/E  OF  A  MAN  THIRTY-SEVEN  YEARS  OF  AGE.    X  180.—  (Schaper.) 


THE    EYE   AND    ITS    APPENDAGES.  357 

interna,  which  is  not  present  in  the  pars  optica  retinae  ;  their  peripheral 
surface  is  joined  to  pigmented  cells,  a  continuation  of  the  pigmented 
epithelium. 

The  pars  iridica  retime,  the  pigment  layer  of  the  iris,  has  been 
described  (p.  347). 

With  regard  to  the  connections  of  the  nervous  elements  of  the  retina, 
according  to  the  foregoing  description  the  nerve -processes  of  the  ganglion- 
cells  of  the  ganglion  of  the  optic  nerve  and  of  the  stellate  cells  of  the 
inner  granule  layer  are  the  centripetal  optic-fibers,  while  the  centrifugal 
nerve-fibers  terminate  in  free  endings  in  the  inner  granule  layer.  The 
ganglion-cells  of  the  ganglion  retinae  apparently  do  not  possess  a  nerve- 
process  ;  their  union  with  the  other  nervous  elements  is  effected  by  means 
of  the  nervous  tangles  in  the  two  reticular  layers,  and  not  only  as  else- 
where by  contact  in  the  customary  manner  (p.  102),  but  also  by  direct 
connection  by  means  of  true  anastomoses.* 

The  connection  with  the  visual  cells  is  effected  by  means  of  the 
intra-epithelial  processes  of  the  cells  of  the  ganglion  retinae,  that  ter- 
minate between  (not  within)  the  visual  elements.  Physiologic  researches 
make  it  highly  probable  that  the  visual-cells  constitute  the  essential 
percipient  part  of  the  retina. 

THE  OPTIC  NERVE. 

The  optic  nerve  in  its  entire  intraorbital  course  is  enveloped  in 
sheaths  which  are  processes  of  the  cerebral  membranes.  Outermost  is 
the  compact  dural  sheath,  consisting  of  longitudinally-disposed  bundles 
of  connective  tissue  (Fig.  266)  ;  following  within  this  is  the  exceedingly 
delicate  arachnoidal  sheath,  which  sends  numerous  relatively  thick  con- 
nective-tissue trabeculae  inward  to  the  pial  sheath,  while  the  union  with  the 
dural  sheath  is  represented  by  a  few  delicate  fibers.  Innermost  lies  the 
pial  sheath,  which  closely  invests  the  optic  nerve  and  sends  numerous 
septa  between  the  individual  nerve-fiber  bundles.  These  septa  are  con- 
nected with  one  another  by  transverse  trabeculae,  the  resultant  structure 
being  a  transverse  lattice-work. 

The  tissue  of  the  pial  sheath  does  not  penetrate  within  the  nerve- 
fiber  bundles,  but  only  forms  an  outer  envelope  for  them.  The  nerve- 
fiber  bundles  consist  of  medullated  fibers  without  a  neurilemma ;  they 
are  held  together  by  many  neuroglia-cells  (spider  cells).  At  the  entrance 
of  the  optic-nerve  into  the  eyeball  the  dural  sheath  passes  into  the  sclera, 

*  Not  shown  in  Fig.  262. 


HISTOLOGY. 


the  arachnoidal  sheath,  at  its  anterior  border,  resolves  into  fibers,  so 
that  the  subdural  space  lying  on  its  outer  side  communicates  with  the 
subarachnoidal  space  on  its  inner  side.  The  pial  sheath  blends  with  the 
sclera,  which  here  is  pierced  with  numerous  apertures  for  the  nerve-fibers 
passing  through  it  ;  this  portion  of  these  sheaths  is  called  lamina  cribrosa. 
The  choroid  also  participates,  though  in  a  slight  degree,  in  the  forma- 
tion of  the  lamina  cribrosa.  The  nerve-fibers  lose  their  medullary  sheath 


Central  artery. 
Fibers  of  lamina  cribrosa.  Central  vein. 


Hyaloid  membrane, 
loosened. 


Retina.  — 
Choroid.  -{ 


Sclera. 


Bundles  of  optic  nerve.  r=^ 

Pial  sheath.    —  -r-j 

Arachnoidal  sheath.    _  _  J 


Dural  sheath. 


i,,!  i  I,-  1 


FIG.  266.—  LONGITUDINAL  SECTION  OF  THE  OPTIC  ENTRANCE  OF  A  HUMAN  EYE.  X  15.  Above  the 
lamina  cribrosa  the  narrowing  of  the  optic  nerve  is  visible.  The  central  artery  and  vein  have  been 
for  the  most  part  cut  longitudinally,  but  above  at  several  points  transversely.  Techn.  No.  169  d. 

at  the   point  of  entrance   and   consequently   the   nerve  is  considerably 
reduced  in  size. 

The  central  artery  and  vein  of  the  retina  lie  in  the  axis  of  the 
distal  half  of  the  optic  nerve  ;  the  connective  tissue  investing  these 
vessels  is  connected  at  many  points  with  the  pial  sheath,  as  well  as  with 
the  lamina  cribrosa. 

THE  LENS. 

The  lens  consists  of  a  substantia  lentis  that  on  its  anterior  surface  is 
covered  by  the  epithelium  of  the  lens  ;  the  whole  is  enveloped  by  the  lens- 
capsule.  In  the  substantia  lentis  a  soft  cortical  substance  and  a  firm  core 
maybe  distinguished  ;  it  consists  throughout  of  colossal,  greatly-elongated 
epithelial-cells,  the  lens-fibers.  They  have  the  form  of  six-sided  pris- 
matic bands,  that  are  thickened  at  their  posterior  extremities.  The 
lens-fibers  of  the  cortical  substance  have  smooth  borders  and  in  the 


THE    EYE    AND    ITS    APPENDAGES. 


359 


vicinity  of  the  equator  lies  an  oval  nucleus.  The  lens-fibers  of  the  central 
portion  of  the  lens  have  dentated  borders  and  are  nonnucleated.  All 
the  fibers  are  united  with  one  another  by  a  small  amount  of  cement- 
substance,  that  is  accumulated  in  larger  quantities  at  the  anterior  and 
posterior  poles  of  the  lens  and  gives  rise  to  the  so-called  anterior  and 
posterior  lens-stars,  stellate  forms  seen  in  macerated  preparations.  All 
the  lens-fibers,  beginning  at  the  anterior  lens-star,  run  in  a  meridional 
direction  to  the  posterior  lens-star  ;  but  no  lens-fiber  spans  the  entire  half 
of  the  lens  ;  the  nearer  the  fibers  arise  to  the  anterior  pole,  the  more 
remote  from  the  posterior  pole  do  they  find  their  termination. 


FIG.  267.— LENS-FIBERS  OF  AN  INFANT.  A. 
Isolated  lens-fibers,  three  with  smooth, 
one  with  dentated  borders.  X  240. 
Techn.  No.  178.  B.  Human  lens-fibers 
cut  transversely  ;  c,  section  through  club- 
shaped  ends.  X  560  Techn.  No.  179. 


FIG.  268.— CAPSULE  AND  EPITHELIUM  OF  AN  ADULT 
HUMAN  LENS.  C.  Inner  aspect.  X  240.  Techn.  No.  i8oa. 
D.  Lateral  aspect,  from  a  meridional  section  through  the 
equator  of  the  lens;  /.  capsule;  2,  epithelium  ;  j,  lens- 
fibers.  X  240.  Techn.  No.  180  b. 


The  lens -epithelium  consists  of  a  simple  layer  of  cubical  cells,  which 
covers  the  anterior  surface  of  the  lens  and  extends  as  far  as  the  equator  ; 
here  the  epithelium,  with  gradual  elongation  of  its  elements,  is  trans- 
formed into  the  lens-fibers  (Fig.  268,  D). 

The  lens-capsule  is  a  transparent,  elastic  membrane;  the  anterior 
capsule,  the  portion  covering  the  anterior  surface  of  the  lens,  is  from  1 1  to 
I  5  fj.  thick,  the  corresponding  posterior  portion,  the  posterior  capsule,  only 
5  to  7  tL  The  lens-capsule  comprises  two  genetically  distinct  parts  ;  the 
one  is  a  cuticular  formation,  a  product  of  the  epithelium  of  the  lens,  the 
other,  partly  of  the  nature  of  connective  tissue,  is  a  transformation 
product  of  the  embryonal  connective-tissue  sheaths. 


HISTOLOGY. 


THE  VITREOUS  BODY. 

The  vitreous  body  consists  of  a  fluid  substance,  the  vitreous  substance, 
and  of  fibers,  which  extend  in  all  directions  through  the  former.  The 
surface  of  the  vitreous  body  is  covered  by  a  firmer  membrane,  the  hyaloid 
membrane,  and  in  certain  localities  contains  a  limited  number  of  fibrilla^ 
and  a  few  cells  ;  of  the  latter  two  forms  maybe  distinguished,  (i)  round 
elements,  resembling  leucocytes,  and  (2)  stellate  and  fusiform  cells.  Cells 
containing  clear  vacuoles  probably  are  degenerating  forms. 


THE  SUSPENSORY  LIGAMENT. 

The  suspensory  ligament  (zonula  ciliaris,  zone  of  Zinn),  consists  of 
delicate  homogeneous  fibers  which  extend  from  the  surface  of  the  hyaloid 
membrane,  in  the  vicinity  of  the  ora  serrata,  in  a  meridional  direction 
toward  the  lens.  They  are  attached  to  the  inner  surface  of  the 
ciliary  processes  and  proceed  from  the  tips  of  the  same  over  to  the 
equator  of  the  lens,  where  they  are  attached  to  the  anterior  and  posterior 
surfaces  and  to  the  equator  of  the  lens-capsule.  The  fibers  do  not  any- 
where form  a  continuous  membrane,  but  are  radially-plicated  extensions 
of  the  hyaloid  membrane  that  find  attachment  on  and  afford  support  to 
the  lens.  The  annular  cleft  between  the  zonula  ciliaris  behind  and  the 
vitreous  body  in  front  is  designated  canal  of  Petit  (spatia  zonularia). 
Other  authors  describe  the  triangular  space  included  between  the  anterior 
and  posterior  zonula  fibers  and  the  lens-capsule  as  the  canal  of  Petit. 
The  canal  is  not  completely  closed  on  the  side  toward  the  posterior 
chamber  of  the  eye. 

THE  BLOOD-VESSELS  OF  THE  EYEBALL. 

The  blood-vessels  of  the  eyeball  are  separated  in  two  sharply-defined 
regions,  which  are  in  communication  only  at  the  entrance  of  the  optic  nerve. 

I.  Territory  of  the  Vasa  Centralia  Retina  (Fig.  269). — The  central 
artery  of  the  retina,  at  a  distance  of  from  15  to  20  millimeters  from  the 
eyeball,  enters  the  axis  of  the  optic  nerve  (a)  and  runs  within  it  to  the 
surface  of  the  optic  entrance.  Here  it  divides  into  two  main  branches, 
of  which  the  one  is  directed  upward,  the  other  downward,  and  each  of 
which  subdividing  supplies  the  entire  pars  optica  retinae  to  the  ora 
serrata.  During  its  course  in  the  optic  nerve  the  artery  gives  off  numer- 
ous small  branches,  which  run  within  the  processes  of  the  pial  sheath 
between  the  nerve-fiber  bundles  and  anastomose  with  small  arteries  (b] 


THE    EYE    AND    ITS    APPENDAGES. 


36i 


that  have  entered  the  sheaths  of  the  nerve  from  the  surrounding  adipose 
tissue  and  also  with  twigs  of  the  short  ciliary  arteries  (at  <r).      In  the  retina 


Cornea, 


FIG.  269.— SCHEME  OF  THE  VESSELS  OF  THE  EYE,  ACCORDING  TO  LEBER.  External  tunic  stippled, 
middle  tunic  white,  internal  tunic  "and  optic  nerve  dotted  crosswise.  Arteries  light.  Veins  dark. 
Region  of  the  central  vessels  of  the  retina  (small  Italic  letters) :  a.  Artery  ;  a',  central  vein  of  retina  ; 
b,  anastomosis  with  vessels  of  the  sheath;  c,  anastomosis  with  branches  of  the  posterior  short  ciliary 
arteries ;  d,  anastomosis  with  choroidal  vessels.  Region  of  the  vessels  of  the  sheath  (large  Italic 
letters):  A.  Inner;  £,  outer  vessels  of  the  sheath.  Region  of  the  posterior  short  ciliary  vessels 
(Italic  numerals):  /.  Arteries;  T7,  veins  (short  posterior  ciliary);  //,  episcleral  arterial;  //',  epi- 
scleral venous  branches  of  the  same ;  ///,  capillaries  of  the  choriocapillaris.  Region  of  the  posterior 
long  ciliary  vessels  (Arabic  numerals):  i.  Posterior  long  ciliary  artery;  2,  circulus  iridis  major  cut 
transversely;  3,  branches  to  the  ciliary  body  ;  4,  branches  to  the  iris.  Region  of  the  anterior  ciliary 
vessels  (Greek  letters):  a,  Artery;  a',  vein  (anterior  ciliary);  ft,  connection  with  the  circulus  iridis 
major;  y,  connection  with  the  choriocapillaris;  8,  arterial ;  <5',  venous  episcleral  branches;  e,  arterial ; 
e',  venous  branches  to  the  scleral  conjunctiva  ;  17,  arterial ;  V,  venous  branches  to  the  cornea!  limbus ; 
V,  vena  vorticosa ;  S,  cross-section  of  the  venous  sinus  of  the  §clera. 


itself  the  artery  breaks  up  into  capillaries,  which  extend  into  the  outer 
reticular  layer.  The  cerebral  layer  of  the  retina  alone  contains  blood- 
vessels ;  in  the  fundus  foveae  the  cerebral  layer  is  wanting  and  with  it 


362  HISTOLOGY. 

the  blood-vessels.  The  veins  proceeding  from  the  capillaries  run  parallel 
with  the  branches  of  the  arteries  and  finally  unite  in  the  vena  ccntralis 
retina  enclosed  within  the  axis  of  the  optic  nerve  (Fig.  269,  a'). 

In  the  embryo  a  twig  from  the  central  artery  of  the  retina,  the 
hyaloid  artery,  passes  through  the  vitreous  body  to  the  posterior  surface 
of  the  lens.  This  artery  atrophies  before  birth,  but  the  canal  which 
transmits  it  may  still  be  found  in  the  vitreous  body  of  the  adult ;  it  is 
called  the  hyaloid  canal. 

II.  Territory  of  the  Vasa  Ciliaria. — This  region  is  characterized  by 
the  complementary  veins  taking  a  course  entirely  different  from  that  of 
the  arteries. 

Of  the  arteries,  the  short  ciliary  arteries  (Fig.  269,  Roman  numerals) 
supply  the  smooth  portion  of  the  choroid,  while  the  long  ciliary  arteries 
(Fig.  269,  Arabic  numerals)  and  the  anterior  ciliary  arteries  (Fig.  269, 
Greek  letters)  are  primarily  destined  for  the  ciliary  body  and  iris. 

The  branches,  about  twenty,  of  the  short  ciliary  arteries  (arteriae 
ciliares  posticae  breves)  penetrate  the  sclera  in  the  vicinity  of  the 
optic  entrance  (I)  ;  after  giving  off  twigs  (II)  which  supply  the 
posterior  half  of  the  surface  of  the  sclera,  the  arteries  break  up 
into  a  narrow-meshed  capillary  network,  the  choriocapillaris  (III).  At 
the  optic  entrance  the  arteries  anastomose  with  branches  of  the  arteria 
centralis  retinae  (Fig.  259,  c)  and  in  this  way  form  the  circular  artery  of 
the  optic  nerve  ;  at  the  ora  serrata  they  anastomose  with  recurrent  twigs 
of  the  long  ciliary  and  of  the  anterior  ciliary  arteries  (for  the  latter 
anastomosis  see  Fig.  269,  Y)- 

The  two  long  ciliary  arteries  (arteriae  ciliares  anticae  longae)  (i)  like- 
wise penetrate  the  sclera  at  the  optic  entrance  ;  the  one  artery  passes  to 
the  nasal,  the  other  to  the  temporal  side  of  the  eyeball,  between  the 
choroid  and  the  sclera  to  the  ciliary  body,  where  each  artery  divides  in 
two  diverging  branches  running  along  the  ciliary  margin  of  the  iris  ;  by 
the  anastomoses  of  these  branches  of  the  two  long  ciliary  arteries  a 
vascular  ring  (2)  is  formed,  the  larger  arterial  circle  of  the  iris  (circulus 
iridis  major)  from  which  numerous  twigs  arise  for  the  ciliary  body  and 
ciliary  processes  (3)  and  for  the  iris  (4).  Near  the  pupillary  margin  of 
the  iris  the  arteries  form  an  incomplete  ring,  the  smaller  arterial  circle 
(circulus  iridis  minor). 

The  anterior  ciliary  arteries  (arteriae  ciliares  anticae)  come  from  the 
arteries  supplying  the  recti  muscles  of  the  eye,  penetrate  the  sclera  near 
the  corneal  margin,  communicate  with  the  larger  arterial  circle  of  the 
iris  (ft)  supply  the  ciliary  muscle,  and  send 'recurrent  branches  to  unite 
with  the  choriocapillaris  (r).  Before  the  anterior  ciliary  arteries  penetrate 


THE    EYE    AND    ITS    APPENDAGES.  363 

the  solera,  they  give  off  twigs  toward  the  back  for  the  anterior  half  of 
the  sclera  (<$),  toward  the  front  to  the  conjunctival  sclera  (?)  and  to  the 
corneal  limbus  (r/).  The  cornea  itself  is  without  blood-vessels  ;  only  at 
the  margin,  in  the  anterior  lamellae  of  the  substantia  propria,  is  there  a 
circumferential  network  of  capillary  loops. 

All  the  veins  run  toward  the  equator,  where  they  converge  to  four 
(more  rarely  five  or  six)  small  stems,  the  whorl  veins  or  vcnce  vorticosce, 
which  forthwith  pierce  the  sclera  (Fig.  269)  and  empty  into  one  of  the 
ophthalmic  veins.  In  addition  to  these  there  are  small  complemental 
veins  that  run  parallel  to  the  short  ciliary  arteries  and  to  the  anterior 
ciliary  arteries,  the  short  ciliary  veins  (Fig.  269,  /'),  and  the  anterior 
ciliary  veins  (#')  ;  the  anterior  ciliary  veins  receive  twigs  from  the  ciliary 
muscle,  from  the  episcleral  vascular  network  (Fig.  269,  #'),  from  the 
conjunctival  sclera  (e7),  and  from  the  circumferential  capillary  loops  of 
the  cornea  (>/).  The  episcleral  veins  also  communicate  with  the  venae 
vorticosse  at  the  equator  (at  F).  The  anterior  ciliary  veins  finally  com- 
municate with  the  sinus  venosus  sclcrce  (Schlemm)  (5).  This  is  a  venous 
wreatli  encircling  the  cornea,  that,  lying  within  the  sclera,  still  possesses 
completely-closed  walls.*  It  takes  up  small  veins  from  the  capillary 
network  of  the  ciliary  muscle. 

THE  LYMPH-CHANNELS  OF  THE  EYEBALL. 

The  eye  possesses  no  proper  lymph-vessels,  but  a  series  of  inter- 
communicating lymph-spaces.  Two  complexes  of  such  spaces  may 
be  distinguished,  an  anterior  and  a  posterior  tract.  The  anterior  tract 
comprises  : — 

1 .  The  lymph-canaliculi  of  the  cornea  and  sclera. 

2.  The  anterior  chamber  of  the  eye,  which,  by  means  of  the  capil- 
lary cleft  between  the  iris  and  the  lens,  communicates  with — 

3.  The  posterior  chamber  of  the  eye.     The  latter  is  in  open  connec- 
tion with — 

4.  The  spatia  zonularia. 

The  last  three  spaces  stand  in  close  relation  to  one  another  and  may 
be  injected  from  the  anterior  chamber. 
The  posterior  tract  includes  :— 

1.  The  hyaloid  canal  (canalis  hyaloideus). 

2.  The  lympli-clefts  between  the  sheaths  of  the  optic  nerve,  the  sub- 

*  The  communication  with  the  anterior  chamber  of  the  eye  formerly  described  is  facti- 
tious ;  the  assertion  that  such  communication  existed  was  based  on  the  fact  that  colored  fluids 
injected  into  the  anterior  chamber  pass  over  into  the  venous-wreath  by  filtration. 


364  HISTOLOGY. 

dural  and  the  subarachnoidal  spaces,  the  narrow  cleft  between  the  choroid 
and  the  sclera,  the  perichoroidal  space,  and  the  spatium  interfasciale 
(Tenon),  which  extends  from  the  dural  sheath  of  the  optic  nerve  to  the 
optic  foramen.  These  spaces  may  be  filled  from  the  subarachnoidal  space 
of  the  brain.  The  content  of  these  spaces  is  a  filtrate  from  the  blood- 
vessels, which  also  permeates  the  vitreous  body.  The  quantity  of  this 
fluid  in  the  perichoroidal  space,  also  in  the  interfascial  space,  normally  is 
exceedingly  scanty.  Both  these  spaces  serve  to  facilitate  the  movements 
of  the  choroid  and  of  the  eyeball  and  may  be  regarded  as  synovial  spaces. 

THE  NERVES  OF  THE  EYEBALL. 

The  nerves  of  the  eyeball  penetrate  the  sclera  in  the  circumference 
of  the  entrance  of  the  optic  nerve  and  run  forward  between  the  outer 
tunic  and  the  choroid  ;  after  giving  to  the  choroid  bundles  provided 
with  ganglion-cells,  they  form  an  annular  plexus  intermingled  with 
ganglion-cells  lying  upon  the  ciliary  body,  the  ciliary  ganglionic  plexus 
(plexus  gangliosus  ciliaris),  from  which  branches  arise  for  the  ciliary 
body,  the  iris,  and  the  cornea.  The  nerves  of  the  ciliary  body  terminate 
in  delicate,  pointed  ends  in  the  blood-vessels  and  in  the  ciliary  muscle, 
partly  between  the  muscle-bundles  in  the  form  of  branched  terminal 


Epithelium. 

Anterior  elastic  lamina. 
I 
Portion  of  substantia  propria.   '  ^ 

FIG.  270.— FROM  A  VERTICAL  SECTION  THROUGH  THE  HUMAN  CORNEA.  X  240.  n.  A  dividing  nerve 
penetrating  the  anterior  basal  membrane;  s,  subepithelial  plexus  beneath  the  cylindrical  cells; 
a,  fibers  of  the  intra-epithelial  plexus  ascending  between  the  epithelial-cells.  Techn.  No.  177. 

twigs,  which  perhaps  subserve  the  muscular  sense,  partly  on  the  scleral 
surface  of  the  ciliary  body  in  the  form  of  a  delicate  plexus.  The  medullated 
nerves  of  the  iris  form  networks  and  lose  their  medullary  sheath  as  they 
pass  to  the  pupillary  margin  ;  their  terminal  ramifications  are  in  part  dis- 
tributed to  the  smooth  muscle-fibers  and  to  the  blood-vessel  walls,  while 
another  portion  forms  a  dense  sensory  plexus  lying  close  beneath  the  an- 
terior iridal  surface.  The  nerves  of  the  cornea  first  enter  the  sclera  and  form 
a  circular  plexus,  the  plexus  annularis,  surrounding  the  corneal  margin, 
from  which  branches  arise  for  the  sclera  and  for  the  cornea.  In  man  the 
twigs  in  the  sclera  terminate  in  spherical  end-bulbs  lying  close  under  the 


THE    EYE    AND    ITS    APPENDAGES.  365 

epithelium  ;  they  are  also  found  in  the  substance  proper  of  the  cornea 
for  a  distance  of  from  one  to  two  millimeters  within  the  corneal  limbus. 
The  branches  that  go  to  the  cornea,  after  their  entrance  in  the  substance 
proper,  lose  their  medullary  sheath  and  as  naked  axis-cylinders  penetrate 
the  entire  structure.  They  form  networks,  which  according  to  the  plane 
they  occupy  are  described  as  the  stroma-  or  ground-plexus,  which  lies  in 
the  deeper  strata  of  the  cornea;  the  sub-basal  plexus,  which  is  situated 
beneath  the  anterior  elastic  lamina  ;  the  sub-epitliclial  plexus,  which  lies 
close  under  the  epithelium.  From  the  latter  plexus  exquisitely-delicate 
nerve-fibril lae  ascend  into  the  epithelium  between  its  elements  and  form 
the  exceedingly  fine  intra-cpitlidial  plexus,  the  ramifications  of  which  ter- 
minate in  free  ends  between  the  epithelial-cells  (Fig.  270). 


THE  EYELIDS. 

The  eyelids,  palpcbrce,  are  folds  of  the  integument,  which  enclose 
muscles,  loose  and  compact  connective  tissue,  and  glands.  The  outer 
fold  of  the  eyelid  retains  the  usual  character  of  the  skin  ;  the  inner  fold, 
that  toward  the  eyeball,  is  considerably  modified  and  is  called  the  palpe- 
bral  conjunctiva.  The  skin  on  the  external  surface  of  the  eyelid  extends 
over  the  anterior  free  margin  of  the  lid  and  does  not  pass  into  the  palpe- 
bral  conjunctiva  until  it  reaches  the  posterior  border,  the  palpcbral 
border. 

The  eyelid  is  best  studied  in  a  sagittal  section  (Fig.  271)  in  which, 
counting  from  before  backward,  the  following  strata  are  found  : 

i.  The  integument  is  thin  and  beset  with  fine  lanugo-hairs,  the  folli- 
cles of  which  it  encloses  ;  in  the  corium  small  coil-glands  are  found,  also 
pigmented  connective-tissue  cells,  that  are  of  rare  occurrence  elsewhere 
in  the  corium.  The  subcutaneous  tissue  is  very  loose,  rich  in  fine  elastic 
fibers,  poor  in  fat-cells,  that  may  be  entirely  wanting.  Near  the  border 
of  the  lid  the  corium  is  more  compact  and  beset  with  more  conspicuous 
papillae.  In  the  anterior  edge  of  the  margin  of  the  lid  two  or  three  rows 
of  robust  hairs,  the  cilia,  are  obliquely  implanted,  the  follicles  of  which 
extend  far  into  the  corium.  The  cilia  undergo  rapid  shedding ;  their 
length  of  life  is  said  to  be  about  from  one  hundred  to  one  hundred  and 
fifty  days  ;  consequently  hairs  in  all  stages  of  development  are  frequently 
found  among  the  eyelashes.  The  hair-follicles  of  the  cilia  are  provided 
with  small  sebaceous  glands,  in  addition  to  which  they  take  up  the 
excretory  ducts  of  the  ciliary  glands  (Moll),  which  in  their  minute 
structure  resemble  coil-glands,  from  which  they  differ  only  in  having 
their  lower  ends  less  convoluted. 


366 


HISTOLOGY. 


2.  Posterior  to  the  subcutaneous  tissue  lie  the  transverse  bundles  of 
cross-striated  muscle-fibers  of  the  orbicularis  palpebrarum  muscle ;    the 
portion  of  the  muscle  lying  behind  the  cilia  (McR)  is  named  the  tarsal 
muscle  (Riolan). 

3.  Behind  the  muscle  the  fibrous  extensions  of  the  tendon  of  the 
levator  palpebrae  muscle  are   met,  which   are  partly  lost  in  the  areolar 
tissue  present,  the  so-called  fascia  palpebralis,  and  partly  attached  to  the 


McR* 


FIG.  271.— SAGITTAL  SECTION  OF  THE  UPPER  EYELID  OF  A  SIX-MONTHS'-OLD  CHILD.  X  10.  i.  Integu- 
ment:  £,  epidermis;  C,  corium  ;  Sc,  subcutaneous  tissue;  Hb,  hair-follicles  of  lanugo  hair;  K,  coil- 
gland  ;  W,  eyelash,  with  the  anlage  of  a  new  hair  (Eh) ;  W1 ,  W" ,  portions  of  follicles  of  eyelashes; 
M,  portion  of  a  ciliary  gland.  2.  Region  of  the  orbicularis  palpebrarum  muscle  :  O,  bundles  of  this 
muscle  cut  transversely  ;  McR,  tarsal  muscle.  3.  Expanded  tendon  of  the  levator  palpebrarum  supe- 
rior :  mps,  superior  palpebrarum  muscle.  4.  Conjunctiva!  portion:  <?,  conjunct!  val  epithelium;  //, 
tunica  propria  ;  at,  accessory  tear-glands ;  /,  tarsus  ;  m,  tarsal  glands,  the  mouth  of  excretory  duct  is 
not  shown ;  a,  transverse  section  of  the  arcus  tarseus ;  a',  transverse  section  of  the  arcus  tarseus 
externus.  5.  Margin  of  eyelid.  Techn.  No.  182. 

upper  margin  of  the  tarsus  ;  the  latter  portion  contains  smooth  muscle- 
fibers  (mps)  the  superior  palpebral  muscle  (Miiller).  In  the  lower  eyelid 
the  expansion  of  the  tendon  of  the  inferior  rectus  muscle  also  contains 
bundles  of  nonstriped  muscle-fibers,  the  inferior  palpebral  muscle. 

4.  The  tarsus  is  a  plate  of  dense  fibrous  tissue,  which  gives  firmness 
and  support  to  the  eyelid.     It  lies  immediately  in  front  of  the  conjunctiva, 


THE    EYE    AND    ITS    APPENDAGES.  367 

to  which  it  belongs,  and  occupies  the  lower  two-thirds  of  the  height  of 
the  entire  eyelid.  In  its  substance  the  tarsal  glands  (Meibom)  (in)  are 
embedded,  elongated  bodies  which  consist  of  a  wide  excretory  duct 
opening  on  the  palpebral  border  and  of  little  follicles  with  short  stalks, 
that  empty  into  it  on  all  sides.  In  their  histology  the  tarsal  glands  agree 
with  the  sebaceous  glands.  At  the  upper  end  of  the  tarsus,  partly 
enclosed  by  its  substance,  lie  branched  tubular  glands  which  in  their 
minute  structure  coincide  with  the  tear-glands  and  therefore  are  called 
accessory  tear-glands  (Fig.  261,  at)  ;  they  principally  occur  in  the  inner 
(nasal)  half  of  the  eyelid. 

Behind  the  tarsus  lies  the  conjunctiva  proper,  which  consists  of  an 
epithelium  (e)  and  a  tunica  propria  (tp).  The  former  is  a  stratified 
columnar  epithelium,  with  several  rows  of  spherical  cells  in  the  depths 
and  a  row  of  mainly  short  cylindrical  cells  on  the  surface.  The  latter 
possess  a  narrow  hyaline  cuticular  border.  Goblet-cells  also  occur  in 
varying  numbers.  At  the  posterior  palpebral  border  the  epithelium 
gradually  passes  into  the  stratified  scaly  variety,  that  occasionally  extends 
far  over  on  the  conjunctiva.  The  lower  portion  of  the  palpebral  con- 
junctiva is  smooth.  In  the  upper  portion,  on  the  contrary,  the  epithe- 
lium forms  irregular  pocket-like  depressions,  the  "  conjunctival  recesses," 
that  differ  greatly  in  individual  development  and  in  sections,  when  highly 
developed,  may  resemble  glands.  The  tunica  propria  of  the  conjunctiva 
consists  of  connective  tissue,  of  plasma-cells  in  varying  number,  and  of 
lymphoid  cells,  the  number  of  which  likewise  varies  greatly.  In  animals, 
especially  in  ruminants,  the  latter  form  true  nodules,  the  so-called 
trachoma  glands,  from  the  summit  of  which  the  leucocytes  wander 
through  the  epithelium  to  the  surface  ;  in  man,  the  migration  of  the 
leucocytes  occurs  in  a  slighter  degree.  In  the  region  of  the  conjunctival 
recesses,  the  tunica  propria  is  divided  into  papillae  by  the  depressions  of 
the  epithelium,  hence  the  name  "  papillary  body." 

The  palpebral  conjunctiva  passes  from  the  eyelids  to  the  eyeball,  the 
anterior  surface  of  which  it  covers.  At  the  point  of  transit,  the  fornix 
conjunctiva,  a  loose  sub-conjunctival  tissue  consisting  of  connective- 
tissue  bundles  occurs  under  the  tunica  propria.  The  epithelium  is  the 
same  as  that  on  the  palpebral  conjunctiva ;  the  tunica  propria  contains 
fewer  leucocytes,  but  also  in  man  normally  possesses  about  twenty  small 
lymph-nodules  and  a  few  mucous  glands.  The  scleral  conjunctiva  is 
modified  in  so  far  that  the  stratified  columnar  epithelium  within  a  certain 
distance  of  the  cornea  is  transformed  into  the  stratified  scaly  variety, 
which  continues  in  that  of  the  cornea. 

The  rudimentary  third  eyelid  (plica  semilunaris)  consists  of  connective 


368  HISTOLOGY. 

tissue  and  stratified  squamous  epithelium.  The  caruncula  lacrimalis 
resembles  the  skin  in  structure,  only  the  stratum  corneum  is  absent,  and 
contains  fine  hairs,  sebaceous  and  accessory  tear-glands. 

The  blood-vessels  of  the  eyelids  proceed  from  branches  that, 
approaching  from  the  outer  and  inner  angles  of  the  eye,  form  an  arch, 
the  arcus  tarscus  (Fig.  271,  a),  at  the  margin  of  the  lid  and  a  second  arch, 
the  arcus  tarscus  extcrnus  (#'),  at  the  upper  end  of  the  tarsus.  Branches 
from  these  arches  ramify  in  the  skin,  surround  the  tarsal  glands,  and 
penetrate  the  tarsus  to  supply  a  capillary  network  lying  beneath  the 
conjunctival  epithelium  ;  they  also  supply  the  fornix  conjunctivas,  the 
scleral  conjunctiva,  and  anastomose  with  the  anterior  ciliary  arteries. 

The  lymph-vessels  form  a  close-meshed  network  in  the  tarsal  conjunc- 
tiva, a  very  open-meshed  network  on  the  anterior  surface  of  the  tarsus. 
According  to  some  authors,  the  lymph-channels  of  the  scleral  conjunctiva 
are  closed  at  the  corneal  limbus  ;  according  to  others,  they  send  minute 
canaliculi  into  the  tissue  of  the  cornea  and  are  in  communication  with 
the  system  of  lymph-spaces  and  canaliculi  in  the  latter. 

The  nerves  form  a  very  dense  plexus  in  the  tarsus  and  in  the  palpe- 
bral  conjunctiva,  which  is  characterized  by  a  peculiar,  coil-like,  twisted 
arrangement  of  its  fibers.  One  portion  of  the  tarsal  plexus  surrounds 
the  tarsal  glands  *  and  here  consists  of  many  nonmedullated  and  few 
medullated  nerve-fibers  ;  another  portion  terminates  in  the  walls  of  the 
blood-vessels.  From  the  "  conjunctival  "  plexus  medullated  nerve-fibers 
arise,  that  run  obliquely  toward  the  margin  of  the  lid  and  the  palpebral 
conjunctiva,  lose  their  medullary  sheath,  in  part  penetrate  directly  into 
the  epithelium,  where  they  branch  and  terminate  in  free  endings,  in  part 
terminate  in  end-bulbs  lying  close  under  the  epithelium.  These  end- 
bulbs  are  found  in  large  numbers  not  only  in  the  papillae  of  the  margin 
of  the  lid  and  in  the  palpebral  conjunctiva,  but  also  in  the  ocular  conjunc- 
tiva and  in  the  margin  of  the  cornea  (see  also  p.  193). 


THE  LACRYMAL  GLANDS. 

The  lacrymal  glands  are  compound  tubular  glands,  provided  with 
several  excretory  ducts.  The  latter  are  clothed  with  a  two-layered 
cylindrical  epithelium  and  pass  into  long,  narrow  intercalated  tubules 
clothed  with  low  epithelial-cells.  These  pass  into  the  gland-tubules,  which 
are  lined  by  serous  gland-cells. 


*  Whether  nerve-fibers  penetrate  between  the  gland-cells  has  not  yet  been  distinguished 
,rith  certainty. 


THE    EYE    AND    ITS    APPENDAGES. 


The  walls  of  the  lacrymal  canaliculi  consist  of  stratified  scaly,  epi- 
thelium, of  a  tunica  propria  rich  in  elastic  fibers,  beneath  the  epithelium 
also  rich  in  cellular  elements,  and  of  cross-striped  muscle-fibers,  for  the 
greater  part  running  longitudinally. 


£*  •«  £--«  •••;»,  °..Y«^T;Y. 


FIG.  272.- FROM  A  THIN  SECTION  OF  A  HUMAN  LACRYMAL  GLAND.  X  240.  A.  Gland;  a,  tubule  cut 
transversely  ;  a',  group  of  tubules,  mostly  cut  obliquely,  the  lumen  of  one  tubule  only  visible  below ; 
s,  intercalated  tubule  with  cubical  (above  to  the  right)  and  flat  (below  to  the  left),  epithelial-cells; 
s',  intercalated  tubule  in  cross-section,  lined  with  moderately  high  cylindrical  cells ;  b,  connective 
tissue.  B.  Cross-section  of  the  duct;  <?,  double  layer  of  cylindrical  epithelium  ;  b,  connective  tissue. 
Teehn.  No.  183. 

The  lacrymal  sac  and  the  naso-lacrymal  duct  consist  of  a  two-lay- 
ered columnar  epithelium  and  of  a  tunica  propria  which  is  chiefly  adenoid 
in  character  and  separated  from  the  underlying  periosteum  by  a  dense 
plexus  of  veins. 

TECHNIC. 

No.  169. — Carefully  cut  the  fresh  eye-ball  out  of  the  optic  cavity 
and  secure  as  much  as  possible  of  the  optic  nerve  ;  then  with  the  scis- 
sors remove  the  attached  fat  and  muscle  and  with  a  sharp  razor  make  an 
incision  at  the  equator,  about  I  cm.  long,  through  all  the  coats  of  the 
eye.  Place  the  eye-ball  in  I  50  c.c.  of  0.05  per  cent,  chromic  acid  solu- 
tion (p.  31) ;  after  from  twelve  to  twenty  hours,  beginning  at  the  incision 
already  made,  divide  the  eye-ball  with  the  scissors  completely  into  an 
anterior  and  posterior  half  and  change  the  fluid.  After  another  twelve  or 
twenty  hours  wash  the  pieces  and  harden  them  in  TOO  c.c.  of  gradually- 
strengthened  alcohol  (p.  33). 

a.  Carefully  remove  the  lens  from  the  anterior  half  of  the  eye-ball 
and  treat  it  further  like  No.  181  ;  then  cut  out  a  quadrant  and  with  the 
attached  ciliary  body  and  iris  embed  it  in  liver  and  cut  sections  through 
the  iridocorncal  angle.     The  thick  sections  are  to  be  stained  with  Hansen's 
hematoxylin  and  mounted  in  damar  (Fig.  258). 

b.  From    the  remaining  three-fourths   of  the  anterior  half  of  the 
eye-ball  cut  out  a  piece  of  the  cornea,  5  or  10  mm.  square,  embed  it  in 
liver    and    make  sections   through   the  layers  of  the  cornea  (Fig.  253). 
The  alternating  lamellae  of  the  substantia  propria  can  only  be  well  seen 
in  unstained  sections  mounted  in  dilute  glycerol. 

24 


3/O  HISTOLOGY. 

c.  From  the  posterior  half  of  the  eye-ball  cut  pieces  including  the 
three  coats,  5  or   10  mm.   square,  and  cut  sections,  not  too  thin,  for  the 
study  of  the  strata  of  the  solera  and  choroid  (Fig.  256).     Stain  them  with 
Hansen's  hematoxylin  (p.  36)  and  mount  in  damar  (p.  45).     In  section- 
ing, the  retina  usually  becomes  loosened. 

d.  For  preparations    showing    the    entrance    of  the    optic-nerve  cut 
around  the  point  of  entrance  at  a  distance  of  about  5   mm.  from   the 
same  through   all  the  coats  of  the  eye  ;   embed  this  portion  with  about 
one   centimeter  of  the  optic-nerve   in  liver    and  cut  sections   (not  too 
thin).      Place  the  knife  so  that  it  strikes  the  retina  first,  then  the  choroid 
and    sclera,   and    passes  through   the  optic-nerve  longitudinally ;  stain 
with  dilute  carmine  (p.  36)  and  with  Hansen's  hematoxylin  (p.  36),  and 
mount  in  damar.      Examine  with  very  low  magnification  (Fig.  266). 

No.  170. — Remove  a  fresh  eye-ball  according  to  the  method  given 
in  No.  169,  make  an  incision  at  the  equator  and  place  it  in  from  100 
to  200  c.c.  of  Muller's  fluid.  In  from  twelve  to  twenty  hours  divide  it 
with  the  scissors  into  an  anterior  and  posterior  half.  In  two  or  three 
weeks  carefully  wash  both  halves  in  slowly  running  water  from  one  to 
two  hours.  Then  cut  pieces  including  all  the  coats  about  8  mm.  long 
and  use  for  them  the  following  preparations  : — 

a.  Teased  Preparation  of  tlie  Choroid, — Tease  and  mount  a  fragment 
in  a  drop  of  dilute   glycerol ;  it  exhibits   large  blood-vessels,  the  capil- 
laries of  the  choriocapillaris,  branched  pigment-cells,  elastic  fibers,  some- 
times also  the  glassy  membrane  ;  the   "  lattice-work  "   of  the  latter  is 
only  partially  distinct.     The  isolated   membranes  may  be   stained  with 
Hansen's  hematoxylin  and  mounted  in  damar,   but   the   more  delicate 
structures  are  thus  rendered  indistinct  (Fig.  257). 

b.  Elements  of  the  Retina. — Carefully   tease  a  small  piece   of  the 
retina  in  a  drop  of  Muller's  fluid.     Along  with   many  fragments  of  the 
elements,  a  few  more  or  less  well-preserved  parts  will  be  found.     Human 
eyes  have  very  large,  beautiful  cone-visual  cells,  while  those  of  many 

,  mammals  are  very  small ;  wholly  unsuitable  in  this  respect  are  the  eyes 
of  the  rabbit ;  unfortunately,  human  eyes  are  usually  no  longer  in  a 
sufficiently  fresh  condition  when  the  investigation  is  made.  The  outer 
segments  of  the  cones,  also  of  the  rods,  are  extremely  delicate  and 
rapidly  disintegrate  after  death,  falling  into  transverse  plates  and  at  the 
same  time  curving  like  a  shepherd's  crook.  Later  they  disappear. 
In  order  to  see  beautiful  cone-visual  cells,  examine,  according  to  the 
method  just  given,  the  eyes  of  fishes.  (See  further,  No.  173  and 

I/4-) 

c.  The  remaining  parts  of  the  eyeball  are  to  be  transferred  from 

the  water  for  hardening  to  80  c.c.  of  gradually-strengthened  alcohol 
(p.  33)  ;  when  the  hardening  is  completed,  cut  out  the  iris,  embed  it  in 
liver,  and  make  meridional  sections  ;  stain  them  in  Hansen's  hematoxylin 
(p.  36)  and  mount  in  damar  (p.  45)  (Fig.  259). 

d.  Cut  out  a  portion  I  cm.  long  of  the  retina,  including  the  ora  ser- 
rata,  which  is  macroscopically  visible  as  a  wavy  line,  embed  it  in  liver, 


THE    EYE   AND    ITS    APPENDAGES.  3/1 

and  make  meridional  sections  ;  stain  them  in  hematoxylin  (p.  36)  and 
mount  in  damar  (Fig.  265). 

c.  Treat  in  the  same  manner  a  piece  of  the  retina  taken  from  the 
posterior  portion  of  the  eye  where  the  optic-fiber  stratum  is  thickest. 
The  radial  fibers  of  Miiller  can  only  be  seen  in  their  entire  length  in 
accurate  vertical  sections  (Fig.  261  and  Fig.  265). 

/.  In  the  same  manner  treat  meridional  sections  through  the  macula 
and  foz'ca.  It  is  not  difficult  to  cut  sections  of  the  macula,  but  on  the 
other  hand  very  difficult  to  obtain  satisfactory  sections  through  the 
extremely  delicate  fovea.  The  retina  should  not  be  loosened  from  the 
choroid,  but  the  two  should  be  sectioned  together.  (Among  the  lower 
mammals  only  the  ape  possesses  a  yellow  macula  and  a  central  fovea  ; 
on  the  other  hand,  the  majority — insectivora  and  certain  rodents  excepted 
— have  an  "  area  centralis,"  without  yellow  pigmentation,  but  similar  in 
structure  to  the  macula.  A  simple  or  multiple  fovea  is  always  present 
in  birds  and  reptiles ;  a  fovea  has  also  been  found  in  bony  fishes.) 

No.  172. — Retina,  after  Golgi. — For  this  purpose  thick  retinae  are 
most  suitable,  therefore  select  the  eyes  of  large  animals.  Divide  the 
eye  into  an  anterior  and  a  posterior  half,  remove  the  vitreous  body,  and 
with  forceps  and  scissors  carefully  dissect  a  piece  of  the  retina  from  the 
choroid.  Cautiously  roll  this  piece  into  a  cylindrical  or  spherical  mass, 
and  dip  it  for  one  second  in  thin  celloidin-solution  ;  expose  it  for  a  few 
seconds  to  the  air,  until  the  envelope  of  celloidin  is  somewhat  stiffened, 
and  then  place  the  piece  in  the  Golgi  mixture  (p.  41).  (The  object  of 
this  envelope  is  to  prevent  the  formation  of  precipitates  on  the  surface.) 
Let  the  object  remain  in  the  Golgi  mixture  for  from  twelve  to  seventy- 
two  hours,  then  transfer  it  for  twenty-four  hours  to  the  silver-solution 
(p.  41).  Then  repeat  the  procedure  (p.  42).  The  impregnation  occurs 
first,  after  twelve  hours,  in  the  rods  and  cones  ;  after  another  twelve 
hours  in  the  bipolar  cells  and  "  spongioblasts  "  (p.  3  51,  remark),  later 
in  the  cells  of  the  ganglion  nervi  optici  and  in  the  nerve-fibers,  last  in 
the  sustentacular  cells. 

No.  173. — Fresh  Elements  of  the  Retina. — Select  the  warm  eyes  of 
animals  just  killed.  Divide  the  eyeball  at  the  equator  and  carefully 
remove  the  vitreous  body  from  the  posterior  half;  cut  small  pieces  about 
3  mm.  square  from  the  transparent  retina  and  tease  in  a  drop  of  the 
vitreous  humor ;  place  two  thin  strips  of  paper  on  either  side  of  the 
preparation  (p.  48),  and  apply  a  cover-glass.  Isolated  elements  will  be 
found  only  here  and  there  ;  on  the  other  hand,  very  good  surface  views 
are  not  infrequently  obtained  in  which  the  rods  and  cones  are  perceptible 
in  optical  cross-section,  the  former  as  small,  the  latter  as  large  circles. 
If  at  the  same  time  a  little  piece  of  the  pigmented  epithelium  has  been 
transferred  to  the  slide,  the  regular  hexagonal  cells  of  the  same  can  be 
plainly  seen  with  the  low  power.  The  light  spots  in  these  cells  are  their 
nuclei  (Fig.  8).  These  cells  are  very  unstable  and  soon  lose  their  sharp 
contours  ;  molecular  motion  of  the  pigment-granules  may  be  very  fre- 
quently observed. 


3/2  HISTOLOGY. 

No.  174. — The  best  method  for  isolating  the  elements  of  tlie  retina 
is  the  following  :  Place  the  eye  unopened,  but  freed  from  fat  and  muscle, 
in  I  per  cent,  osmium  solution.  In  twenty-four  hours  cut  the  eye  open 
at  the  equator  and  place  it  for  maceration  for  two  or  three  days  in  dis- 
tilled water  ;  then  with  scissors  cut  out  a  piece  of  the  retina  about  2  mm. 
long  and  tease  it  in  a  drop  of  water ;  the  preparation  may  be  stained 
under  the  cover-glass  with  picrocarmine  (p.  48)  and  mounted  in  dilute 
glycerol.  With  the  high  power,  in  addition  to  many  fragments  the 
source  of  which  is  not  always  to  be  determined  with  certainty,  elements 
like  those  pictured  in  Fig.  263  may  be  found. 

It  is  advisable  to  select  the  eyes  of  small  animals — e.  g.,  a  small 
water  salamander — in  which  the  sclera  is  thin  and  allows  the  osmium 
solution  to  penetrate  easily.  For  such  an  eye  i  or  2  c.c.  of  the  solution 
will  be  sufficient.  The  form  of  the  rods  is  quite  different  from  those  of 
mammals  ;  they  are  thick  and  are  provided  with  long  outer  segments  ; 
the  cones  are  small. 

No.  175. — Corneal Spaces  and  Canaliculi. — Select  an  eye  as  fresh 
as  possible  ;  of  the  eyes  of  animals,  that  of  the  ox  is  most  suitable  ;  with 
the  handle  of  a  scalpel  scrape  away  the  epithelium  of  the  cornea  ;  spray 
the  denuded  surface  with  distilled  water  ;  cut  through  the  eye  in  front 
of  the  attachment  of  the  ocular  muscles  and  place  the  anterior  segment 
containing  the  entire  cornea  down  on  the  epithelial  side  ;  then  with  for- 
ceps and  scalpel  remove  the  ciliary  body,  the  lens,  and  the  iris,  so  that  only 
the  anterior  portion  of  the  sclera  and  the  cornea  remain,  which  are  to  be 
placed  in  40  c.c.  of  a  I  per  cent,  solution  of  silver  nitrate.  The  whole  is  then 
placed  in  the  dark  for  from  three  to  six  hours  and  then  transferred  to  50 
c.c.  of  distilled  water  and  exposed  to  sunlight  (see  further,  p.  40).  Harden 
the  objects  in  50  c.c.  of  gradually-strengthened  alcohol  and  cut  horizontal 
sections,  which  are  most  easily  obtained  if  the  cornea  is  held  over  the 
left  index-finger.  It  is  best  to  take  the  sections  on  the  posterior  surface 
of  the  cornea,  since  the  spaces  and  canaliculi  are  more  regular  there. 
The  sections  may  be  stained  in  Hansen's  hematoxylin  and  mounted  in 
damar.  The  pictures  are  negative,  the  spaces  and  canaliculi  white 
on  a  brown  or  brown-yellow  surface  (Fig.  254).  Carefully  examine 
the  usually  somewhat  thinner  margins  of  the  section  ;  in  sections  stained 
in  hematoxylin  the  nuclei  of  the  fixed  corneal  corpuscles  are  a  dull  blue  ; 
the  contours  of  the  cells  can  seldom  be  perceived. 

NO<  176. — Fixed  Corneal  Corpuscles  by  the  Gold  Method. — The 
method  described  on  page  43  is  to  be  somewhat  modified,  as  follows  : 
Express  the  juice  from  a  fresh  lemon  ;  filter  it  through  flannel.  Kill  the 
animal,*  cut  out  the  cornea  and  place  it  for  five  minutes  in  the  lemon-juice, 
in  which  it  becomes  transparent ;  then  wash  it  in  5  c.c.  of  distilled  water  for 
one  minute  ;  transfer  it  to  10  c.c.  of  gold-chlorid  (p.  22)  solution  and  place 
it  in  the  dark  for  fifteen  minutes.  With  glass  rods  transfer  the  cornea  to 

*  Frogs  are  especially  recommended ;  their  corneal  canaliculi  are  very  regular  and  their 
posterior  lamina  is  easily  detached. 


THE    EYE    AND    ITS    APPENDAGES.  373 

10  c.c.  of  distilled  water  for  one  minute,  then  to  50  c.c.  of  distilled  water 
to  which  2  drops  of  acetic  acid  have  been  added,  and  expose  it  to  day- 
light ;  in  from  twenty-four  to  forty-eight  hours  the  reduction  is  com- 
pleted. The  object  is  then  to  be  placed  in  10  c.c.  of  70  per  cent,  alcohol 
(in  the  dark)  ;  on  the  following  day  cut  out  a  little  piece  of  the  cornea, 
hold  it  with  needle  and  scalpel  at  the  edges  and  separate  the  thin  lamellae 
from  the  posterior  surface  ;  with  a  little  attention  this  can  be  successfully 
done  without  much  trouble.  Mount  the  lamellae  in  damar. 

No.  177. — Very  good  preparations  of  the  corneal  canaliculi  are 
obtained  by  the  method  of  Drasch.  The  objects  are  not  to  be  taken  from 
the  animal  recently  killed,  but  twelve  or  twenty -four  hours  after  death, 
during  which  time  the  cadaver  must  be  kept  in  a  cool  place.  Small  pieces  of 
the  corneaare  to  be  cut  out,  about  6  mm.  long,  placed  in  5  c.c.  of  i  per  cent, 
gold-chlorid  solution  plus  5  c.c.  of  distilled  water,  and  stood  in  the  dark 
for  one  hour ;  during  this  time  frequently  stir  the  fluid  with  a  glass 
rod.  With  glass  rods  transfer  the  pieces  to  30  c.c.  ol  distilled  water, 
in  which  they  should  remain  (in  the  dark)  for  from  eight  to 
sixteen  hours.  They  are  then  to  be  transferred  to  25  c.c.  of  distilled 
water  plus  5  c.c.  of  formic  acid  and  exposed  to  daylight.  When  the  re- 
duction is  completed  (p.  43)  the  dark-violet  pieces  are  to  be  hardened  in 
gradually-strengthened  alcohol  and  in  about  six  days  thin  sections 
parallel  to  the  surface  can  be  cut  and  mounted  in  damar  (Fig.  254). 

No.  178. — Nerves  and  Blood-vessels  of  the  Fresh  Cornea. — Select  the 
eye  of  an  ox  and  cut  out  the  cornea  and  the  adjoining  portion  of  the 
sclera  extending  from  the  limbus  to  the  attachment  of  the  ocular  muscles  ; 
with  scalpel  and  forceps  remove  the  ciliary  body,  iris,  and  lens,  immedi- 
ately cut  out  a  quadrant  of  the  cornea,  place  it  with  the  epithelial  side  up 
on  a  slide  and  apply  a  cover-glass  ;  a  drop  of  the  vitreous  humor  may  be 
added.  The  very  thick  preparation  must  be  examined  with  a  low  power. 
When  the  surface  of  the  cornea  is  in  focus  the  loop-shaped  blood-vessels 
can  be  seen  at  the  scleral  margin  ;  the  majority  still  contain  blood-cor- 
puscles. Medullated  nerve-fibers  are  found  here,  as  well  as  in  the  deeper 
strata ;  they  are  arranged  in  bundles  and  within  the  cornea  can  only  be 
traced  for  a  short  distance.  The  elongated  pigment-streaks  found  in  the 
eye  of  the  ox  have  no  relation  to  the  nerves. 

This  method  is  not  serviceable  for  the  exhibition  of  the  finer  distri- 
bution of  the  nerves. 

No.  179. — Nerves  of  the  Cornea. — a.  Gold  Method. — Cut  out  the 
cornea  twelve  or  twenty-four  hours  after  death,  remove  the  ciliary  body 
and  iris,  and  treat  it  according  to  the  method  given  in  No.  176.  When 
the  hardening  is  completed  cut  horizontal  sections,  which  contain  the 
epithelium  and  the  uppermost  strata  of  the  cornea,  and  vertical  sections 
through  the  thickness  of  the  cornea.  Mount  in  damar  (Fig.  270). 

b.  Methylene  Blue  Staining. — Kill  a  rabbit ;  remove  the  entire  eye- 
ball, free  it  from  the  attached  remnants  of  ocular  muscles  and  connective- 
tissue,  place  it  in  a  watch-glass  and  with  a  sharp  scalpel  make  a  deep 


374  HISTOLOGY. 

incision  through  all  the  coats  of  the  eye  at  the  equator  ;  thus  the  vitreous 
humor  escapes  into  the  watch-glass.  Then  with  scissors  separate  from 
the  point  of  incision  the  entire  cornea,  place  it  on  a  slide  with  the  con- 
cave surface  upward  and  with  the  handle  of  the  scalpel  scrape  off  the 
ciliary  body,  iris,  and  lens,  which  is  easily  done  ;  transfer  the  cornea 
thus  cleansed  to  a  second  watch-glass  containing  from  3  to  10  drops  of 
the  vitreous  humor  and  from  3  to  4  drops  of  a  -fa  per  cent,  methylene 
blue  solution  (p.  25).  The  concave  surface  of  the  cornea  should  be 
uppermost  and  covered  by  the  staining  fluid. 

The  time  required  for  staining  cannot  be  given  with  certainty  ;  there- 
fore it  is  advisable  after  several  hours  to  place  the  cornea  with  the  convex 
surface  up  on  a  clean  slide  and,  without  a  cover-glass,  to  examine  it  with 
the  low  power  ;  if  it  is  not  sufficiently  stained  return  it  to  the  watch- 
glass  and  examine  it  again  in  about  ten  minutes. 

So  soon  as  the  nerves  can  be  distinctly  seen  the  cornea  is  to  be 
transferred  for  from  eighteen  to  twenty  hours  to  20  c.c.  of  the  ammonia 
solution  (p.  39) ;  then  cut  out  a  quadrant  and  mount  it  in  dilute  glycerol, 
to  which  a  drop  of  the  ammonia-solution  has  been  added  ;  after  being 
kept  in  the  dark  for  twenty-four  hours  the  preparation  is  sufficiently 
transparent  and  can  be  investigated  with  the  high  power. 

No.  1 80. — Lens-fibers. — Cut  the  eye-ball  open  back  of  the  equator  ; 
remove  the  vitreous  body  and  lens ;  thus  the  pigment  covering  the 
ciliary  processes  remains  attached  to  the  margin  of  the  lens.  Loosen 
the  lens  from  the  vitreous  body  and  place  it  in  50  c.c.  of  Ranvier's 
alcohol  (p.  20).  In  about  two  hours  thrust  needles  into  the  anterior  and 
posterior  surfaces  of  the  lens  and  strip  the  capsule  up  from  a  small  area  ; 
this  is  easily  done  ;  if  lens-fibers  are  attached  to  the  capsule  it  does  not 
matter.  On  pricking  the  lens  a  turbid  white  fluid  escapes  ;  shake  the 
alcohol  and  let  the  lens  remain  in  it  for  from  ten  to  forty  hours.  At  the 
expiration  of  this  time  the  lens  can  be  easily  separated  into  shell-like 
pieces.  Tease  a  small  strip  of  one  of  these  pieces  in  a  small  drop  of  salt 
solution  on  a  slide  (p.  19).  Apply  a  cover-glass,  taking  care  to  avoid 
pressure  ;  if  it  is  desired  to  preserve  the  fibers,  stain  with  picrocarmine 
(staining  usually  occurs  in  a  few  minutes),  and  mount  in  dilute  acidulated 
glycerol  (Fig.  267,  A ). 

•  No.  1 8 1. — Lens-fibers  in  Transverse  Section. — Place  a  lens  in  50  c.c. 
of  0.05  per  cent,  chromic  acid.  A  cloth  or  a  little  cotton  must  be  placed 
on  the  bottom  of  the  bottle  or  the  lens  will  adhere  to  the  glass  and  burst. 
This  may  also  be  prevented  by  frequently  shaking  the  bottle.  In  from 
twenty -four  to  forty-eight  hours  with  a  needle  break  the  lens  into  shell- 
like  pieces,  transfer  them  after  ten  or  fifteen  hours  to  30  c.c.  of  70  per 
cent,  alcohol,  which  is  to  be  replaced  on  the  following  day  by  an  equal 
quantity  of  90  per  cent,  alcohol.  With  the  scissors  cut  the  pieces  through 
in  the  region  of  the  equator,  and  so  embed  them  in  liver  that  the  first  sec- 
tions will  pass  through  the  zone  lying  next  to  the  equator.  If  the  section, 
which  need  not  be  very  thin,  has  passed  through  the  fibers  transversely 
they  will  appear  as  sharply- defined  hexagons  ;  if,  on  the  contrary,  the 


THE    EYE    AND    ITS    APPENDAGES.  375 

section  is  oblique,  the  single  fibers  will  appear  to  be  separated  from  one 
another  by  irregular  zigzag  lines  ;  they  may  even  be  cut  partially  length- 
wise. The  sections  are  to  be  transferred  directly  from  the  blade  to  the 
slide  and  mounted  in  dilute  glycerol  (Fig.  267,  B). 

No.  182. — The  Lens  Capsule  and  the  Lens  Epithelium. — Place  the 
eyeball,  free  from  muscle  and  fat,  in  100  or  200  c.c.  of  Muller's  fluid. 
Treat  it  further  as  follows  : 

a.  Surface  View  of  the  Lens  Capsule  and  Epithelium. — After  two  or 
three  days  cut  the  eye  open,  remove  the  lens,  and  with  forceps  strip  off 
a  piece  of  the  anterior  lens  capsule  ;  place  it  for  about  five  minutes  in  a 
watch-glass  with  distilled  water,  which  is  to  be  changed  once,  then  stain 
it  in  Hansen's  hematoxylin  ;  mount  in  damar.     The  capsule  is  stained  a 
homogeneous  light  blue  ;  the  nuclei  and  contours  of  the  epithelial-cells 
are  very  sharp  (Fig.  268,  C).     If  it  is  desired  to  obtain  the  lens  capsule 
alone  strip  off  a  portion  of  the  posterior  lens  capsule. 

b.  Sections  of  the  Capsule  and  Epithelium. — Let  the  eye-ball  remain 
in  Muller's  fluid  for  two  weeks  ;  remove  the  lens,  wash  it  for  one  hour  in 
running  water  and  harden  it  in  50  c.c.  of  gradually-strengthened  alcohol 
(p.  33);  cut  meridional  sections  through  the  anterior  surface  and  the 
equator  of  the  lens  ;  stain  them  with  Hansen's  hematoxylin  (p.  36)  and 
mount  in  damar  (Fig.  268,  D). 

No.  183. — T/ie  Blood-vessels  of  the  Eye. — For  this  purpose  surface 
preparations  are  especially  suitable.  Open  a  fresh  eye  at  the  equator. 
The  course  of  the  central  artery  of  the  retina  is  macroscopically  percep- 
tible. For  the  exhibition  of  the  blood-vessels  of  the  choroid  place  an 
eyeball  completely  freed  from  attached  muscle  and  fat  on  a  small  glass 
funnel,  which  has  been  thrust  into  a  low  glass  bottle,  and  with  scissors 
and  forceps,  beginning  at  the  equator,  carefully  dissect  off  the  sclera. 
With  a  little  practice  the  entire  sclera  can  be  removed  beyond  the  ora 
serrata  up  to  the  optic  entrance  without  injury  to  the  choroid  ;  care  must 
be  taken  not  to  tear  it.  (Beginners  should  be  content  to  remove  only 
one  quadrant  of  the  sclera.)  All  the  firmer  points  of  attachment 
between  the  sclera  and  choroid  (the  venae  vorticosae)  must  be  cut  through. 
Then  by  careful  brushing  with  a  sable  pencil  moistened  in  water  remove 
the  attached  portions  of  the  lamina  suprachoroidea  from  the  choroid  ; 
by  this  manipulation  the  course  of  the  larger  blood-vessels  is  brought  to 
view.  So  far  the  investigation  may  be  pursued  on  the  uninjected  eye 
(compare  with  No.  170,  a).  For  the  study  of  the  blood-vessels  of  the 
ciliary  body  and  the  iris  it  is  necessary  to  use  an  injected  eye,  divided 
anterior  to  the  equator,  fixed  in  Muller's  fluid  and  hardened  in  alcohol. 
The  iris  and  ciliary  body  may  be  easily  stripped  from  the  sclera ;  remove 
the  lens  and  mount  in  damar.  Examine  at  first  with  the  low  power. 

No.  184. — Place  the  upper  eyelid  of  a  child  in  100  c.c.  of  0.5  chromic 
acid  for  from  one  to  three  days,  wash  it  two  hours  in  running  water,  and 
harden  in  50  c.c.  of  gradually-strengthened  alcohol.  For  a  general  view  cut 


3/6  HISTOLOGY. 

thick  (Fig.  271),  for  the  finer  details  thin  sections  (Fig.  25,  C).  Staining 
with  Hansen's  hematoxylin  is  at  first  difficult,  but  more  readily  accom- 
plished after  the  object  has  lain  in  alcohol  several  months  (compare 
p.  36,  remark  *).  Mount  in  damar. 

No.  185. — The  Lacrymal  Glands. — The  lower  tear-gland  in  man 
can  be  easily  removed,  without  visible  external  injury,  from  the  fornix  of 
the  conjunctiva.  In  the  rabbit  this  gland  is  very  small  and  when  fresh 
resembles  pale  muscle  tissue.  It  must  not  be  confused  with  Harder' s 
gland  lying  in  the  median  angle  of  the  eye.  Treat  like  No.  112. 
Small  pieces  I  mm.  square  can  be  used.  The  excretory  duct  and  tubules 
may  be  easily  seen  ;  difficult,  on  the  other  hand,  it  is  to  see  the  inter- 
calated tubules,  the  epithelium  of  which  differs  greatly  in  height  and 
occasionally  is  so  low  that  care  must  be  taken  not  to  confuse  them  with 
blood-vessels  (Fig.  272). 


XII.  THE  ORGAN  OF  HEARING. 

The  organ  of  hearing  consists  of  three  divisions  ;  the  innermost,  the 
internal  car,  encloses  the  end-apparatus  of  the  auditory  nerve  ;  the  other 
divisions,  the  middle  ear  and  the  external  ear,  are  only  accessory  appara- 
tus. 

THE   INTERNAL  EAR. 

The  internal  ear  consists  of  two  membranous  saccules  lying  within 
the  bony  vestibule  (vestibulum),  that  communicate  with  each  other  by 
means  of  a  minute  canal,  the  ductus  utriculo-saccularis.  The  one  saccule, 
the  utricle,  is  in  connection  with  membranous  tubules,  the  semicircular 
canals  (ductus  semicirculares),  each  of  which  at  the  point  where  it  opens 
in  the  utricle  possesses  a  dilatation,  the  ampulla.  The  other  saccule, 
the  sacculus,  connects  by  means  of  the  ductus  reuniens  with  a  long 
spirally-wound  membranous  sack,  the  cochlea  (ductus  cochlearis). 

The  sacculus  and  utriculus,  the  semicircular  canals  and  the  cochlea 
are  called  the  membranous  labyrinth.  This  is  enclosed  within  the  petrous 
bone  in  a  space  having  similar  outlines,  the  bony  labyrinth,  which  it  does 
not  completely  fill.  The  unfilled  space  is  occupied  by  a  watery  fluid, 
the  perilymph.  A  similar  fluid,  the  endolymph,  is  contained  within  the 
interior  of  the  membranous  labyrinth. 

The  saccules  and  the  semicircular  canals  exhibit  the  same  struct- 
ure, but  the  cochlea  is  so  essentially  different  that  it  requires  a  separate 
description. 

THE  SACCULE,  THE  UTRICLE,  AND  THE  SEMICIRCULAR  CANALS. 
The  walls  of  these  canals  comprise  three  layers.  The  outermost  is 
a  connective -tissue  layer  rich  in  elastic  fibers  ;  this  is  followed  within  by 
a  delicate  basal  membrane  beset  with  minute  excrescences,  which  on  its 
inner  surface  is  covered  by  a  simple  squamous  epithelium.  This  simple 
structure  undergoes  alteration  at  the  positions  where  the  filaments  of  the 
auditory  nerve  are  distributed,  the  macnlcz  cribroscz  of  the  saccule  and 
utricle,  the  cristce  acusticce  on  the  ampullae  of  the  semicircular  canals. 
The  connective  tissue  and  basal  membrane  here  become  thicker ;  the 
squamous  epithelium  already  in  the  vicinity  of  the  maculae  and  cristae 

377 


3/8  HISTOLOGY. 

becomes  transformed  into  a  columnar  epithelium  with  a  cuticular  border, 
and  this  passes  into  the  neuro-epithelium  of  the  maculae  and  cristae. 
The  neuro-epithelium  likewise  is  a  simple  layer  and  consists  of  two  kinds 
of  cells  :  (i)  fiber-cells,  elongated  elements  occupying  the  entire  depth 
of  the  epithelium,  slightly  expanded  at  the  upper  as  well  as  at  the  lower 
end,  and  containing  an  oval  nucleus  ;  they  are  the  sustentacular  elements  ; 
(2)  hair-cells,  cylindrical  elements  occupying  only  the  upper  half  of  the 
epithelium,  which  in  their  lower  rounded  division  contain  a  large  spheri- 
cal nucleus  and  bear  on  their  free  surface  a  bundle  of  long,  delicate 
agglutinated  filaments,  the  "  auditory  hairs."  The  hair-cells  are  the  ter- 
minal apparatus  of  the  auditory  nerve.  The  nerve-fibers  of  the  ramus 
vestibularis  nervi  acustici  are  in  connection  with  the  hair-cells  and  in  this 
-way.  On  entering  the  epithelium  the  nerve-fibers  lose  their  medullary 
sheath,  divide,  and  as  naked  axis-cylinders  ascend  to  the  base  of  the 
hair-cells  ;  there  each  fiber  divides  into  three  or  four  varicose  twigs,  that 
run  beneath  several  hair-cells  parallel  to  the  surface  of  the  epithelium, 
and  finally  turn  upward  and  terminate  in  contact  with  the  lateral  surface 
of  a  hair-cell  in  a  free  pointed  end.*  During  their  horizontal  course 
they  send  upward  a  few  twigs,  that  in  the  same  manner  end  in  contact 

with  the  hair-cells.     These  ends  do  not  reach  to  the 

£?  surface  of  the  epithelium.     The  free  surface  of  the 

^0  neuro-epithelium  is  covered  by  a  continuation  of  the 

^  0  ^p  cuticular   zone,  a  "limitans,"  which  is   perforated  by 

r\         the  auditory  hairs.     The  maculae  acusticae  are  covered 

by  a  soft  substance  (a  cuticula  ?),  in  which  innumerable 

FIFROM'™TSACCUI!US     prismatic  crystals  of  calcium  carbonate,  the  otoliths, 

TecAhn!NNoT86X56°'     from  I  to  I  5  fJL  in  size,  are  embedded;  they  form  the 

"  otoconia,"  the  auditory  sand.  On  the  cristae  acus- 
ticae the  so-called  cupula  occurs,  in  fresh  preparations  an  invisible  sub- 
stance, that  on  the  application  of  fixation  fluids  coagulates  and  thus 
becomes  visible. 

By  means  of  strands  of  connective  tissue  the  saccules  and  the  semi- 
circular canals  are  secured  to  the  bony  labyrinth,  the  inner  surface  of 
which  is  covered  by  a  thin  periosteum  and  flattened  connective-tissue 
cells. 

THE  COCHLEA. 

The  membranous  cochlea,  the  ductus  cochlcaris,  does  not  entirely  fill 
the  space  within  the  bony  cochlea.  It  lies  with  one  wall  in  contact  with 

*  The  horizontal  branches  interlace  and  form  a  small,  but  dense  "lattice-work,"  that  also 
by  other  methods  than  that  of  Golgi  appears  to  consist  of  a  special  layer  of  strongly -refracting 
granules.  The  granules  are  the  varicosities  and  the  optical  cross-sections  of  the  horizontal 
fibers. 


THE    ORGAN    OF    HEARING. 


379 


the  outer  wall  *  of  the  bony  cochlea  (Fig.  274)  ;  the  upper  or  vestibular 
wall,  the  vestibular  incinbratie  (Reissner),  bounds  the  scala  vestibuli ;  the 
lower  or  tympanic  wall,  the  membranous  spiral  lamina,  is  directed  toward 
the  scala  tympani.  The  angle  in  which  the  vestibular  and  tympanic 
wall  meet  lies  on  the  free  end  of  the  osseous  spiral  lamina.  There  the 
periosteum  and  the  connective  tissue  of  the  ductus  cochlearis  are  espe- 
cially well  developed  and  form  a  prominence,  the  limbus  spiralis,  which 
rests  with  a  broad  surface  on  the  bony  spiral  lamina,  slopes  upward 
and  terminates  in  a  sharp  edge.  This  edge  is  called  the  labium  vestibu- 
lare,  the  free  margin  of  the  bony  spiral  lamina  is  called  the  labium 


Limbus  spiralis. 


Membrana 
s.  vestibularis.  Ductus  cochlearis. 


Bony  axis  of  the  cochlea 
(modiolus). 


Ganglion  spirale. 


Organ  of  Corti  (organon 
spirale). 


(j)      Outer  bony  wall   of  the 

cochlea. 
Vas  prominens. 


• •    Ligamentum  spirale. 


Lamina  spiralis  mem- 
branacea. 


Lamina  spiralis  ossea, 

FIG.  274.— SECTION  THROUGH  THE  SECOND  TURN  OF  THE  COCHLEA  OF  AN  INFANT.  X  25.  The  modiolus 
contains  longitudinal  canals  cut  obliquely,  s.  Bony  wall  between  the  second  and  third  (half)  turns 
of  the  cochlea.  The  membrana  vestibularis  is  torn  through,  the  upper  fragment  being  turned  up- 
wards. The  membrana  tectoria  could  not  be  seen.  Techn.  No.  188. 

tympanicunt,  between  the  two  runs  the  sulcus  spiralis  (Fig.  280).  The 
inner  surfaces  of  the  ductus  cochlearis  are  covered  by  an  epithelium  that 
varies  greatly  in  different  localities  ;  the  outer  surfaces,  toward  the  scala 
vestibuli  and  scala  tympani,  are  covered  by  a  delicate  continuation  of  the 
periosteum  which  clothes  both  scalae.  On  the  outer  wall  of  the  cochlea 
the  periosteum  becomes  greatly  thickened  and  in  cross-section  appears 
as  a  crescentic  mass,  the  ligamentum  spirale,  that  extends  above  and 
below  the  attached  surface  of  the  ductus  cochlearis  (Fig.  274). 

The  minute  structure  of  the  outer  and  the  vestibular  wall  of  the 


*  I  here  follow  the  customary  description,  in  which  the  cochlea  is  placed  in  such  a  manner 
that  the  base  is  directed  downward,  the  summit  upward  ;  accordingly,  "inner"  is  toward  the 
axis  of  the  cochlea,  "  outer  "  toward  the  periphery. 


380  HISTOLOGY. 

membranous  cochlea  is  comparatively  simple,  that  of  the  tympanic  wall, 
on  the  other  hand,  is  extremely  complicated. 

The  outer  watt  and  the  spiral  ligament  together  consist  of  epithelium 
and  connective  tissue.  The  latter,  next  to  the  bone,  is  a  dense  fibrous 
tissue  (the  periosteum)  ;  this  passes  into  a  loose  connective  tissue  which 
contributes  the  chief  bulk  of  the  spiral  ligament.  The  epithelium  con- 
sists of  a  row  of  cubical  epithelial  cells.  A  dense  network  of  blood- 
vessels, the  stria  vascularis,  occupies  three-fourths  of  the  height  of  the 
outer  cochlear  wall,  and  at  its  lower  end  is  limited  by  a  vein  that  projects 
farther  into  the  lumen  of  the  cochlea,  the  prominentia  spiralis  (vas  promi- 
nens)(Fig.  274).  The  capillaries  of  the  stria  vascularis  lie  close  beneath 
the  epithelium  ;  they  are  the  source  of  the  endolymph. 

The  vestibular  ivall,  membrana  vestibularis  (Reissner)  (Fig.  274), 
consists  of  a  process  of  the  periosteum  of  the  scala  vestibuli,  that  is, 
of  delicate  fibrous  connective  tissue  and  flattened  cells,  which  on  the 
surface  turned  toward  the  ductus  cochlearis  is  clothed  with  a  simple 
layer  of  polygonal  epithelial  cells. 

The  tympanic  wall  consists  of  two  portions,  (i)  the  limbus,  with  the 
free  margin  of  the  bony  spiral  lamina,  and  (2)  the  lamina  spiralis  mcin- 
branacea. 

The  limbus  consists  of  compact  connective  tissue,  containing  an 
abundance  of  spindle-shaped  cells,  which  below  is  continuous  with  the 

Labium  tympanicum. 

~~~SS£*T?TM..^,          /j  Foramina  nervina. 

P^'fti!     Zona  perforata. 
Labium  vestibulare.  (  VJ 

I  -^=-    Auditory  teeth. 

/o^'^5^Z^rr^ssr—     Papillae. 

FIG.  275.— A  SURFACE  VIEW  OF  THE  LAMINA  SPIRALIS  OF  A  CAT.  X  240.  The  vestibular  lamina  is  seen 
from  above ;  between  the  auditory  teeth  two  nuclei  of  the  epithelial-cells  are  seen.  On  the  left  of  the 
picture  the  plane  of  the  auditory  teeth  is  in  focus,  on  the  right,  the  plane  of  the  zona  perforata. 
Techn.  No.  187. 

tissue  of  the  periosteum,  on  its  free  surface  is  beset  with  peculiarly- 
shaped  papillae.  They  have  the  form  of  an  irregular  hemisphere ; 
toward  the  labium  vestibulare  they  develop  into  small,  elongated  plates, 
the  so-called  auditory  teeth  (Fig.  275  and  Fig.  278),  that  lie  in  a  single 
row  beside  one  another.  The  surface  of  the  limbus  is  covered  by  a 
simple  layer  of  flattened  epithelial  cells,  which  at  the  edge  of  the 
labium  vestibulare  passes  into  the  cubical  epithelium  of  the  sulcus 
spiralis  (Fig.  278,  A). 

The  upper  surface  of  the  free  margin  of  the  osseous  spiral  lamina  is 


THE    ORGAN    OF    HEARING. 


perforated  by  a  single  row  of  slit-like  openings,  the  foramina  nervina 
(Fig.  275),  through  which  the  nerves  enclosed  within  the  bony  lamina 
emerge,  to  penetrate  within  the  epithelium  of  the  lamina  spiralis  mem- 
branacea.  This  portion  of  the  osseous  spiral  lamina 
is  called  zona  perforata. 

The  membranous  spiral  lamina  (lamina  spiralis 
membranacea)  consists  of  (i)the  membrana  basil- 
aris, an  extension  of  the  limbus  and  of  the  perios- 
teum of  the  osseous  spiral  lamina,  (2)  the  tympanic 
lamella,  a  process  of  the  periosteum  of  the  scala 
tympani  which  clothes  the  lower  surface  of  the 
basilar  membrane,  and  (3)  the  epithelium  of  the 
ductus  coclilearis,  which  rests  upon  the  upper  sur- 
face of  the  basilar  membrane. 

The  membrana  basilaris  consists  of  a  struct- 
ureless substance  which  contains  rigid,  perfectly 
straight  fibers,  extending  from  the  labium  tym- 
panicum  to  the  spiral  ligament,  and  of  oblong 
nuclei.  The  membrane  has  a  finely-striated  appearance  (Fig.  276,  y). 

The  tympanic  lamella  consists  of  a  delicate  connective  tissue  contain- 
ing spindle-cells,  the  fibers  of  which  are  disposed  vertically  to  the 
elements  of  the  basilar  membrane  (Fig.  276,  b). 

The  cpitlielium  of  that  half  of  the  membranous  spiral  lamina  toward 


FIG.  276.— SURFACE  VIEW 
OF  THE  LAMINA  SPIRALIS 
MEMBRANACEA  OF  A  CAT. 
X  240.  Strata  of  the  zona 
pectinata  drawn  with 
change  of  focus,  e.  Indif- 
ferent epithelium  (cells  of 
Claudius)  of  the  ductus 
cochlearis  in  focus ;  f,  the 
fibers  of  the  membrana 
basilaris  in  focus ;  £,  the 
nuclei  of  the  tympanic 
lamella  in  focus.  Techn. 
No.  185. 


Cells  of  Claudius. 

Fibers. 

Outer  hair-cells. 

Pillar-cells. 

Inner  hair-cells. 


Zona  pectinata. 


-    Zona  tectoria 

Labium  tympanlcum. 
Labium  vestibulare. 


l    , 
J 


Ganglion  spirale. 


FIG.  277. — LAMINA  SPIRALIS  OF  A  CAT  SEEN  FROM  THE  VESTIBULAR  SURFACE.  The  membrana  tectoria 
has  been  removed.  X  50.  lo.  Lamina  spiralis  ossea,  inner  half  cracked  and  broken  at  several 
points;  at  the  posterior  border  of  the  same  cells  of  the  spiral  ganglion  project  forth.  Int.  Lamina 
spiralis  membranacea.  The  cells  of  Claudius  have  partly  fallen  off,  so  that  the  fibers  of  the  mem- 
brana basilaris  are  seen  as  a  delicate  striation.  Techn.  No.  187. 


the  axis  of  the  cochlea  is  differentiated  as  the  highly-specialized  neuro- 
epithelium  of  the  spiral  organ  (organ  of  Corti),  while  that  occupying  the 
outer  half,  toward  the  spiral  ligament,  consists  of  indifferent  epithelial 


382 


HISTOLOGY. 


elements.  Therefore  the  spiral  lamina  is  divided  into  two  zones  :  an 
inner,  occupied  by  the  spiral  organ,  zona  tccta,  and  an  outer,  zona 
pectinata,  so  called  because  of  the  striations  of  the  basilar  membrane 
shimmering  through  it. 

The  most  remarkable  elements  of  the  spiral  organ  are  the  pillar- 
cells,  peculiarly-shaped,  for  the  greater  part  rigid  forms,  arranged  in  two 
rows  the  entire  length  of  the  cochlea.  'The  inner  row  of  pillar-cells 
form  the  inner  pillars,  the  outer  row,  the  outer  pillars  (Fig.  278).  The  two 


FIG.  278. — SCHEME  OF  THE  STRUCTURE  OF  THE  TYMPANIC  WALL  OF  THE  DUCT  OF  THE  COCHLEA. 
A.  Seen  from  the  side.  B.  Seen  from  the  surface.  In  the  latter,  the  free  surface  is  in  focus.  It  is 
evident  that  the  epithelium  of  the  sulcus  spiralis,  lying  in  another  plane,  as  well  as  the  cells  of 
Claudius,  can  only  be  distinctly  shown  by  depressing  the  tube.  The  membrana  tectoria  is  not 
drawn.  The  spiral  nerve-bundles  are  indicated  by  dots. 


rows  of  pillars  are  obliquely  inclined  toward  one  another  and  form  an 
arch,  the  arcus  spiralis,  which  spans  a  triangular  space,  the  tunnel,  the 
base  of  which  is  directed  toward  the  basilar  membrane.  The  tunnel  is 
nothing  more  than  a  very  large  intercellular  space,  that  is  filled  with 
a  soft  mass,  the  intercellular  substance.  Regarding  the  histology  of 
the  pillar-cells,  the  following  details  are  to  be  considered  :  The  inner 
pillar-cells  are  rigid  bands,  in  which  a  three-sided  expanded  foot,  a  slender 
body,  and  a  concave  head,  with  the  concavity  directed  outward,  may  be 


THE    ORGAN    OF    HEARING.  383 

distinguished.  The  head  is  furnished  with  a  thin  process,  the  "  head- 
plate  "  (Fig.  278).  The  body  and  foot  of  the  cell  are  surrounded  by  a 
scant  amount  of  protoplasm,  that  only  to  the  outer  side  of  the  foot  in 
the  vicinity  of  the  nucleus  is  present  in  somewhat  larger  amount.  The 
outer  pillar-cells  exhibit  the  same  details,  excepting  that  the  portion  con- 
taining the  nucleus  lies  to  the  inner  side  of  the  foot ;  the  rounded 
articular  head  rests  in  the  concave  facet  of  the  head  of  the  inner  pillar- 
cells,  the  broader  head-plate  is  covered  in  its  greater  part  by  the  head- 
plate  of  the  inner  pillars.  To  the  inner  side  of  the  inner  pillars  lies  a 
simple  row  of  cells,  the  inner  Jiair-cells,  short  cylindrical  elements  that  do 
not  extend  to  the  basilar  membrane  ;  they  possess  a  rounded  base  and 
about  forty  stiff  hairs  on  their  free  surface.  To  the  inner  side  of  the 
inner  hair-cells  lies  the  cubical  epithelium  of  the  sulcus  spiralis.  On  the 
outer  side  of  the  outer  pillars  lie  the  outer  Jiair-cells  ;  they  resemble  the 
inner  hair-cells,  but  possess  hairs  that  are  one-third  shorter  and  are  char- 


FIG.  279.— SURFACE  VIEW  OF  THE  LAMINA  SPIRALIS  MEMBRANACEA  OF  A  CAT.  X  240.  A.  Outer  pillar- 
cells  ;  k,  head-plates  of  the  same,  upper  surface  in  focus ;  a/>,  body  and  inferior  extremity  drawn  with 
gradual  depression  of  the  tube ;  kip,  portions  of  the  head-plates  of  the  inner  pillar-cells.  B.  It. 
Labium  tympanicum  partly  covered  by  the  epithelium  of  the  sulcus  spiralis ;  th,  inner,  ah,  outer  hair- 
cells,  between  these  the  phalanges,  ^/t,  forming  the  membrana  reticularis ;  ap,  head-plates  of  the 
outer,  ip,  of  the  inner  pillar-cells.  Techn.  No.  187. 

acterized  by  a  dark  body  occupying  the  upper  half  of  the  cell,  the  spiral 
body*  The  outer  hair-cells  are  arranged  in  several  (usually  four)  rows  ; 
they  do  not  lie  in  contact  with  one  another,  but  are  held  apart  by 
Dciters's  cells  ;  these  are  elongated  cells  that  contain  a  rigid  filament  and 
at  their  upper  end  support  a  cuticular  top-plate,  which  has  the  form  of  a 
digital  phalanx.  The  free  spaces  between  the  "  phalanges  "  are  occupied 
by  the  upper  ends  of  the  outer  hair-cells  f  (Fig.  279).  The  cells  of 
Deiters  are  sustentacular  elements,  that  exhibit  much  in  common  with 
the  pillar-cells  ;  like  these  they  consist  of  a  rigid  filament  and  a  proto- 

*  In  the  scheme  (Fig.  278,  A]  this  body  is  indicated  by  a  dark  speck  close  beneath  the 
auditory  hairs. 

f  The  inner  hair-cells  are  kept  apart  from  one  another  by  short  processes  of  the  inner 
pillar-cells.  These  processes  are  not  shown  in  Fig.  278,  B. 


HISTOLOGY. 


plasmic  portion,  like  these  they  have  a  head-plate  (named  phalanx). 
The  difference  consists  only  in  this,  that  the  transformation  into  rigid 
parts  is  not  so  far  advanced  in  the  cells  of  Deiters.  The  phalanges  are 
joined  to  one  another  and  form  a  beautiful  netted  membrane,  the  mem- 
brana  reticularis. 

The  outer  hair-cells  do  not  extend  to  the  basilar  membrane,  but 
occupy  only  the  upper  half  of  the  spaces  between  the  cells  of  Deiters  ; 
the  lower  divisions  of  these  spaces  remain  unoccupied,  and  are  called 
Nuel's  spaces  or,  since  they  communicate  with  one  another,  the  space  of 
Nuel  (Fig.  278,  A).  The  latter  also  has  the  significance  of  an  intercel- 
lular space  and  is  connected  with  the  tunnel. 

External  to  the  last  row  of  Deiters's  cells  lie  the   cells   of  Hensen, 


Nerves. 


Labium         Pillar-cells.  ^ > — ' 
tympanicum.  Tympanic  lamella. 


Lamina  spiralis  ossea. 


Organ  of  Corti. 


FIG.  280. — VERTICAL  RADIAL  SECTION  THROUGH  THE  PERIPHERAL  HALF  OF  THE  LAMINA  SPIRALIS 
OSSEA  AND  THROUGH  THE  LAMINA  SPIRALIS  MEMBRANACEA  OF  AN  INFANT.  X  80.  The  membrana 
tectoria  has  been  torn  from  its  point  of  attachment  on  the  labium  vestibulare.  Techn.  No.  188. 


elongated  cylinders,  that  gradually  decrease  in  height  and  pass  into  the 
indifferent  epithelium  of  the  cochlear  duct,  the  elements  of  which,  so  far 
as  they  cover  the  basilar  membrane,  are  called  the  cells  of  Claudius. 

A  soft,  elastic  cuticular  formation,  the  membrana  tectoria,  lies  above 
the  sulcus  spiralis  and  the  spiral  organ  (Fig.  280).  It  is  attached  to  the 
vestibular  lip  of  the  sulcus  and  extends  to  the  outermost  row  of  hair- 
cells. 

The  cochlear  branch  of  the  auditory  nerve  penetrates  into  the  axis  of 
the  cochlea  and  in  its  spiral  uninterrupted  ascent  gives  off  branches 
which  pass  to  the  root  of  the  osseous  spiral  lamina  ;  here  each  medul- 
lated  nerve-fiber  loses  its  medullated  sheath  and  passes  into  a  nerve-cell 
that  like  those  of  the  spinal  ganglia  possesses  a  connective-tissue  capsule  ; 


THE    ORGAN    OF    HEARING.  385 

these  nerve-cells  collectively  form  the  ganglion  spirale*  which  winds 
along  the  entire  periphery  of  the  axis  of  the  cochlea  (Fig.  274) ;  from 
the  opposite  pole  of  each  cell  springs  a  second  nerve-fiber,  that  soon 
acquires  a  medullated  sheath  and  unites  with  neighboring  fibers  in  a 
wide-meshed  plexus  enclosed  within  the  osseous  spiral  lamina ;  this 
plexus  extends  near  to  the  labium  tympanicum,  where  the  fibers  lose 
their  medullated  sheath,  escape  through  the  foramina  nervina  and  end 
in  the  epithelium.  This  occurs  in  such  a  manner  that  they  bend  in  the 
direction  of  the  circumvolution  of  the  cochlea  and  run  in  spiral  bundles, 
of  which  the  first  passes  to  the  inner  side  of  the  inner  pillar-cells,  the 
second  into  the  tunnel,  the  third  between  the  outer  pillar-cells  and  the 
first  row  of  the  cells  of  Deiters,  the  remaining  three  between  the  cells  of 
Deiters.  From  these  bundles  delicate  fibers  proceed  to  the  hair-cells, 
on  which  (not  within)  they  terminate. 

The  Arteries  of  the  Labyrinth. — The  auditory  artery  gives  only  a  small 
twig  to  the  membranous  labyrinth  and  another  small  twig  to  the  bony 
labyrinth  ;  the  majority  of  its  branches  pass  to  the  roots  of  the  fifth, 
seventh,  eighth,  ninth,  and  tenth  cranial  nerves  and  to  the  under  surface 
of  the  cerebellum.  The  artery  for  the  membranous  labyrinth  divides 
into  two  branches  :  i.  The  arteria  vestibularis  (Fig.  281)  sends  twigs  to 
the  vestibular  nerve  and  to  the  lateral  upper  half  of  the  sacculus  and 
utriculus,  as  well  as  to  the  corresponding  portions  of  the  upper  and 
lateral  semicircular  canal,  which  supply  a  capillary  plexus  that  in  general 
is  wide-meshed,  but  at  the  terminal  points  of  the  vestibular  nerve,  the 
cristae  and  maculae,  is  narrow-meshed.  2.  The  arteria  cochlearis  com- 
munis  divides  in  two  branches.  The  one  branch,  the  arteria  vestibulo- 
cochlearis,  supplies  one  twig  to  the  median-posterior  half  of  the  sacculus, 
utriculus,  and  semicircular  canals  and  in  its  minute  ramifications  behaves 
like  the  vestibular  artery  ;  another  twig  ramifies  in  the  initial  third  of  the 
first  turn  of  the  cochlea.  The  other  branch,  the  arteria  cochlearis  pro- 
pria,  supplies  the  remaining  extent  of  the  cochlea ;  on  entering  the  axis 
of  the  cochlea  it  divides  into  three  or  four  branches,  which  in  their 
spiral  ascent  form  the  tractus  arteriosus  spiralis.  From  this  about 
30  or  35  radial  twigs  arise,  which  supply  three  separate  capillary  terri- 
tories :  (i)  the  canal  in  which  the  ganglion  spirale  is  enclosed,  (2) 
the  lamina  spiralis,  (3)  the  intermediate  and  outer  walls  of  the  scalae 
(Fig.  282,  i,  2,  3). 

*  The  ganglion  spirale  possesses  the  same  structure  as  the  spinal  ganglia,  with  a  single 
difference, — the  ganglion-cells  are  not  unipolar,  but  bipolar,  as  in  the  embryonal  ganglia.  The 
ganglion  vestibulare  in  the  interior  of  the  cochlea  also  possesses  bipolar  ganglion-cells. 

25 


386 


HISTOLOGY. 


The  veins  of  the  labyrinth  follow  three  separate  paths  : 

1.  The  vena  aquceductus  vestibuli    runs    through    the    aquaeductus 
vestibuli  ;    it  collects  the  blood   from  the  semicircular  canals  and  from 
one  portion  of  the  utriculus  ;  it  opens  in  the  sinus  pretrosus   superior 
(Fig.  281). 

2.  The  vena    aquczductus   cocldece    runs    through    the    aquaeductus 


Arteriae 
labyrinth,  "i     Arteria  cochlearis  communis. 


Arteria  vestibularis. 

Ampulla 
superior. 


Ductus  semicircularis 
superior. 

Ampulla  lateralis. 


Vena  aquaeductus 

vestibuli. 

Ductus  semicircularis 
lateralis.     . 


Arteria  cochlearis 
propria. 

Arteria  vestibulo-cochlearis.  Vena  spiralis. 


Superior      Inferior     Anterior 


Posterior 


Vena  vestibularis. 


Ampulla 
posterior. 


Ductus  semicircularis 
posterior. 


Arteria  cochlearis  communis. 


Vena  aquaeductus  cochleae 


FIG.  281.— SCHEME.  BLOOD-VESSELS  OF  THE  RIGHT  HUMAN  LABYRINTH.  MEDIAN  AND  POSTERIOR 
ASPECT  D.  c.  Ductus  cochlearis.  S.  Sacculus.  U.  Utriculus.  i.  Ductus  reuniens.  2.  Ductus 
utriculo-saccularis.  The  saccus  endolymphaticus  is  cut  off. 


cochleae  ;  it  collects  the  blood  from  one  portion  of  the  utriculus,  from 
the  sacculus  and  from  the  cochlea.  The  venous  radicles  in  the  cochlea 
behave  in  the  following  manner  :  The  veins  collecting  at  the  vas  proin- 
inens  and  at  the  vas,  spirale  (Fig.  282,  a,  b)  pass  in  the  wall  of  the  scala 
tympani  to  the  spirally-running  vena  spiralis,  lying  below  the  spiral 
ganglion  ;  this  originates  from  the  confluence  of  two  veins,  of  which  the 


THE    ORGAN    »F    HEARING. 


387 


lower  receives  the  blood  from  the  first  (basal)  and  a  portion  of  the  second 
turn  of  the  cochlea,  while  the  upper  spiral  vein  collects  the  blood  from 
the  remaining  cochlear  turns.  The  spiral  vein  also  takes  up  one  set  of 
the  capillaries  in  the  canal  of  the  spiral  ganglion  and  is  united  by  anas- 
tomosis with  a  vein  lying  above  this  canal,  the  vena  lamina  spiralis 
(Fig.  282).  This  receives  the  blood  from  the  other  set  of  capillaries  of 

Scala  tympani.    Scala  vestibuli. 


Stria  vascularis 


Cross-section  of  an  artery  of  the 
tractus  spiralis. 


,-VenaJamina  spiralis. 


Ganglion  spirale. 


Vena  spiralis  superior. 


Cross-section  of  an  artery  of  the 
tractus  spiralis. 


-Vena  lamina  spiralis. 

Anastomosis. 

"  Vena  spiralis  inferior. 

FIG.  282.— SCHEME.     VERTICAL  SECTION  OF  THE  RIGHT  HALF  OF  THE  FIRST  (BASAL)  AND  SECOND 
TURNS  OF  THE  COCHLEA,     a.  Vas  prominens.    b.  Vas  spirale. 

the  spiral  ganglion,  as  well  as  from  the  lamina  spiralis,*  and  opens  in 
the  central  vein  of  the  cochlea. 

3.  The  central  vein  of  the  cochlea  is  the  main  radicle  of  the  internal 
auditory  vein.  The  latter  takes  up  veins  from  the  auditory  nerve  and 
from  the  bone,  and  in  all  probability  opens  in  the  vena  spinalis  anterior. 

T/ic  Lympli-clianncls. — The  endolymph  in  the  interior  of  the  mem- 

*  The  vestibular  membrane  is  nonvascular  in  the  adult.  The  arrangement  of  the  blood- 
vessels in  the  cochlea  is  such  that  the  scala  vestibuli  is  chiefly  encircled  by  arteries,  the  scali 
tympani  mainly  by  veins.  The  portion  of  the  scala  tympani  adjacent  to  the  lamina  spiralis 
membranacea  is  thus  removed  from  the  influence  of  arterial  pulsation. 


388  HISTOLOGY. 

branous  labyrinth  is  connected  with  the  subdural  lymph-spaces  by  means 
of  minute  canals  passing  from  the  ductus  endolymphaticus.  The  peri- 
lymphatic  spaces  (see  p.  185)  are  in  connection  with  the  subarachnoidal 
space  by  means  of  a  lymph-vessel  running  through  the  aquaeductus 
cochleae,  the  "  ductus  perilymphaticus."  Blood-vessels  and  nerves  are 
surrounded  by  conspicuous  perivascular  and  perineural  lymph-spaces,  that 
probably  also  are  connected  with  the  subarachnoidal  space. 

THE  MIDDLE  EAR. 

The  mucous  membrane  of  the  tympanic  cavity  is  intimately  united 
with  the  underlying  periosteum.  It  consists  of  thin  connective  tissue  and 
a  single  stratum  of  cubical  epithelial-cells,  that  sometimes  on  the  floor, 
occasionally  also  in  larger  areas  of  the  tympanic  cavity,  are  ciliated. 
Glands  (short,  o.  I  mm.  long  follicles)  occur  sparingly  in  the  anterior  half 
of  the  tympanic  cavity.  The  mucosa  of  the  eustachian  tube  consists  of  a 
fibrillar  connective  tissue  (containing  numerous  leucocytes  near  the 
pharyngeal  orifice)  and  of  a  stratified  ciliated  columnar  epithelium  ;  the 
ciliary  wave  is  directed  toward  the  pharynx.  Mucous  glands  occur  in 
especial  abundance  in  the  pharyngeal  half  of  the  tube.  The  cartilage 
of  the  eustachian  tube,  where  it  adjoins  the  bony  tube,  is  of  the  hyaline 
variety  and  here  and  there  contains  rigid  (not  elastic)  fibers  (cf.  p.  83)  ; 
in  the  anterior  portion  the  matrix  of  the  cartilage  is  penetrated  by  dense 
networks  of  elastic  fibers.  The  blood-vessels  in  the  mucosa  of  the  tym- 
panic cavity  form  a  wide-meshed,  in  the  mucosa  of  the  eustachian  tube  a 
narrow-meshed  superficial  capillary  network  and  a  deep  capillary  plexus 
surrounding  the  glands.  The  lymph-vessels  run  in  the  periosteum  of  the 
tympanic  cavity.  With  regard  to  the  terminations  of  the  nerves,  exact 
information  is  still  wanting. 

THE  EXTERNAL  EAR. 

The  tympanum  consists  of  a  lamina  of  connective  tissue,  lamina 
propria,  in  which  the  fibrous  bundles  on  the  outer  side  are  radially 
arranged  and  connected  with  the  periosteum  of  the  sulcus  tympanicus, 
while  on  the  inner  side,  toward  the  tympanic  cavity,  the  fibrous  bun- 
dles are  circularly  arranged.  On  its  inner  surface  the  tympanum  is  cov- 
ered by  the  mucous  membrane  of  the  tympanic  cavity,  on  its  outer  sur- 
face by  the  integument  of  the  external  auditory  canal.  Both  investments 
are  very  firmly  attached  to  the  lamina  propria,  are  smooth,  and  are  with- 
out papillae.  Where  the  malleus  lies  against  the  tympanum,  the  latter  is 
provided  with  a  superficial  stratum  of  hyaline  cartilage. 

The  external  auditory  canal,  so  far  as  it  is  cartilaginous  and  on  the 


THE    ORGAN    OF    HEARING. 


389 


whole  length  of  its  upper  wall,  is  clothed  with  an  extension  of  the  skin, 
which  is  characterized  by  its  thickness  and  by  a  great  abundance  of 
peculiar  coil-glands,  the  ccntminous glands.  In  some  respects  these  glands 
correspond  with  the  ordinary  larger  coil-glands  (sweat-glands)  of  the 
skin  ;  like  these,  they  possess  an  excretory  duct  lined  by  several  layers 
of  epithelial-cells,  and  the  tubules  of  the  coil  contain  a  simple  layer  of 
cubical  gland-cells,  which  rest  on  smooth  muscle-fibers  and  a  conspicu- 
ous basement  membrane  (Fig.  284)  ;  they  are  distinguished  from  the 
sweat-glands  by  the  very  wide  lumen  of  the  coiled  tubule,  that  particu- 
larly in  adults  is  greatly  dilated,  and  by  numerous  pigment-granules  and 
fat-droplets  within  the  gland-cells,  which  frequently  exhibit  a  distinct 


Hair-follicle. £ 

Coriuni.       — :i 


Excretory  duct. 


Young  hair.    — ^ 


Coil  of  ceruminous    <j 
gland. 


FIG.  283. — FROM  A  VERTICAL  SECTION 
THROUGH  THE  SKIN  OF  THE  EXTERNAL 
AUDITORY  MEATUS  OF  AN  INFANT.  X  50. 
The  excretory  duct  opens  into  the  hair- 
follicle.  Techn.  No.  191. 


Membrana  propria. 

Nuclei  of  smooth  muscle-fibers. 

Secretion. 

Gland-cells. 


Secretion. 


, —  Cuticular  border. 
Gland-cells. 

Nuclei  of  smooth  muscle- 
fibers. 
Membrana  propria. 

FIG.  284.— A.  CROSS-SECTION  OF  A  COIL-TUBULE 

OF    THE    SKIN     OF     THE     EXTERNAL     AUDITORY 

MEATUS  OF  AN  INFANT.  B.  LONGITUDINAL 
SECTION  OF  A  COIL-TUBULE  FROM  THE  EXTER- 
NAL AUDITORY  MEATUS  OF  A  TWELVE-YEAR- 
OLD  BOY.  X  240.  Techn.  No.  191. 


cuticular  border.  The  excretory  ducts  are  narrow  and  in  children  open 
in  the  hair-follicles,  in  adults,  close  beside  the  hair-follicles  on  the  free 
surface.  The  secretion,  the  cerumen,  consists  of  pigment-granules,  oil- 
globules,  and  cells  containing  fat ;  the  latter  probably  come  from  the 
sebaceous  glands  of  the  hair-follicles.  In  the  (remaining)  region  of  the 
bony  external  auditory  meatus,  the  integument  is  thin  and  without  ceru- 
minous glands. 

The  cartilage  of  the  external  auditory  canal  and  of  the  pinna  is  of 
the  yellow  elastic  variety. 

The  blood-vessels  and  nerves  are  distributed  as  elsewhere  in  the  skin  ; 
only  on  the  tympanum  do  they  exhibit  peculiarities.  Close  behind  the 


39O  HISTOLOGY. 

handle  of  the  malleus  an  artery  descends,  which  breaks  up  into  radially- 
disposed  branches  ;  the  blood  is  returned  by  two  paths  :  (i)  by  a  venous 
plexus  extending  along  the  handle  of  the  malleus  and  (2)  by  a  venous 
plexus  lying  on  the  margin  of  the  tympanum. 

These  vessels  lie  in  the  integumentary  covering  of  the  tympanum. 
The  mucous  membrane  of  the  tympanum  is  provided  with  a  dense  capil- 
lary network,  which  anastomoses  with  the  integumentary  vascular  net- 
work by  means  of  perforating  branches  at  the  margin  of  the  tympanum. 

The  lymph-vessels  are  principally  found  in  the  cutaneous  stratum  ot 
the  tympanum. 

The  nerves  form  delicate  networks  lying  beneath  the  mucous  and 
the  cutaneous  covers. 

TECHNIC. 

A  fundamental  condition  is  an  exact  knowledge  of  the  macroscopic 
anatomy  of  the  labyrinth.  The  difficulties,  the  failures,  depend  in  the 
main  on  inaccurate  knowledge  of  the  bony  labyrinth.  As  a  preliminary 
all  parts  lying  lateral  to  the  promontory  (os  tympanicum  and  ossicles  of 
the  ear)  must  be  removed,  so  that  this  is  distinctly  visible. 

No.  1 86. — Otoliths. — Chisel  out  the  promontory,  beginning  at  the 
upper  margin  of  the  fenestra  stapedii,  to  the  lower  margin  of  the  fenestra 
rotunda.  Then,  especially  if  the  bone  is  placed  in  water,  the  white  spots 
(maculae)  in  the  sacculus  and  utriculus  can  be  detected.  With  delicate 
forceps  lift  out  the  saccules  and  spread  out  a  small  piece  in  diluted  gly- 
cerol  on  a  slide.  The  otoliths  are  present  in  large  numbers,  but  are 
very  small,  so  that  their  shape  can  only  be  distinctly  seen  with  the  high 
power  (240  diameters).  The  glycerol  must  not  be  too  thick,  or  it  will 
render  the  otoliths  completely  invisible  (Fig.  273). 

In  taking  out  the  saccules  portions  of  the  semicircular  canals  are 
not  infrequently  also  removed  ;  stain  these  with  picrocarmine  and  mount 
them  in  dilute  glycerol.  Only  the  epithelium  and  here  and  there  in 
optical  section  the  delicate  glassy  membrane  can  be  seen.  The  connec- 
tive tissue  is  scanty. 

No.  187. — The  Cochlea. — The  base  of  the  cochlea  lies  in  the  bottom 
of  the  internal  auditory  meatus,  the  apex  is  directed  toward  the  eusta- 
chian  tube,  therefore  the  axis  of  the  cochlea  is  horizontal  and  transverse 
to  the  long  axis  of  the  petrous  bone. 

Open  the  free  portion  of  the  cochlea,  that  is,  remove  the  promon- 
tory close  to  the  fenestra  rotunda,  open  the  apex  of  the  cochlea  and 
having  removed  the  superfluous  osseous  mass  as  far  as  practicable  place 
the  preparation  in  20  c.c.  of  0.5  per  cent,  osmic  acid  (5  c.c.  of  2  percent, 
osmic  acid  to  15  c.c.  of  distilled  water).  In  from  twelve  to  twenty  hours 
wash  the  preparation  for  about  one  hour  and  then  place  it  in  200  c.c.  of 
Miiller's  fluid.  In  from  three  to  twenty  days  (or  later)  open  the  cochlea 


THE    ORGAN    OF    HEARING.  39! 

and  examine  it  in  water.  The  osseous  spiral  lamina  can  be  seen  as  a 
delicate  lamella,  the  membranous  spiral  lamina  as  a  delicate  membrane, 
attached  to  the  axis  of  the  cochlea  ;  with  fine  forceps  break  off  pieces  of 
the  osseous  spiral  lamina  ;  do  not  lift  them  with  the  forceps,  but  carefully 
with  needle  and  section  lifter  remove  them  from  the  fluid  and  transfer 
them  to  a  drop  of  dilute  glycerol  on  a  slide.  It  is  advisable  to  break  ofT 
the  axial  portion  of  the  spiral  lamina  on  the  slide  with  needles,  because 
the  relatively  thick  osseous  process  renders  it  difficult  to  apply  a  cover- 
glass.  The  vestibular  surface  must  be  directed  upward  ;  it  may  be  recog- 
inzed  by  the  auditory  teeth,  which  are  visible  when  the  upper  surface  is 
in  focus  (Fig.  275),  while  the  other  portions  are  not  distinct  until  the 
tube  is  depressed  and  the  lower  planes  are  focused.  With  the  low 
power  only  the  interstices  of  the  auditory  teeth  are  at  first  visible  as 
dark  lines  (Fig.  277,  labium  vestibulare) ;  the  papillae 'likewise  cannot  be 
seen  immediately,  even  with  the  high  power,  but  become  distinct  after 
the  second  or  third  day.  The  chief  difficulty  lies  not  in  the  finishing, 
but  in  the  proper  examination  of  the  object ;  the  picture  alters  with  the 
slightest  change  in  focus.  In  Fig.  278,  B,  the  membranous  spiral 
lamina  is  drawn  schematically,  as  seen  with  the  upper  surface  in  focus, 
therefore  only  the  free  surface  of  the  structure,  drawn  as  seen  from  the 
side  in  A,  is  visible.  It  is  clear  that  in  depressing  the  tube  the  head- 
plates  of  the  pillar-cells  are  no  longer  visible,  but  their  bodies  (as  circles 
in  optical  section) ;  the  reticular  membrane  likewise  disappears  and  can 
be  seen  only  when  the  tube  is  elevated.  The  preparation  may  be  stained 
with  picrocarmine  and  preserved  in  dilute  glycerol.  The  foregoing  direc- 
tions are  intended  to  apply  to  the  human  ear  and  that  of  the  cat.  The 
labyrinths  of  children  are  recommended. 

No.  1 8 8. — Sections  of  the  Bony  and  Membranous  Cochlea. — Remove 
the  cochlea  of  a  child  from  the  labyrinth.  The  compact  osseous  sub- 
stance of  the  cochlea  is  surrounded  by  spongy  bone  so  soft  that  the  latter 
may  be  removed  with  a  stout  penknife.  Having  done  this,  with  a  chisel 
make  small  openings  in  the  cochlea  at  two  or  three  places,  about  I  mm. 
square,  in  order  to  facilitate  the  penetration  of  the  fixation  fluid.  Then 
place  the  cochlea  in  15  c.c.  of  distilled  water  plus  5  c.c.  of  2  per  cent, 
osmic  acid.  After  twenty-four  hours  remove  the  object,  wash  it  for  a 
quarter  of  an  hour  in  running  water,  and  harden  it  in  about  60  c.c.  of 
gradually-strengthened  alcohol.  When  the  hardening  is  completed  de- 
calcify the  cochlea  in  the  following  mixture  :  I  c.c.  of  a  I  per  cent, 
aqueous  solution  of  palladium  chlorid,  10  c.c.  of  hydrochloric  acid,  and 
100  c.c.  of  distilled  water.  Place  the  cochlea  in  100  c.c.  of  this  mixture, 
which  must  be  frequently  changed.  When  the  decalcification  is  com- 
pleted the  object  should  be  again  hardened,  embedded  in  liver,  and  sec- 
tioned. The  sections  must  be  made  in  the  long  axis  of  the  cochlea. 
Stain  them  with  picrocarmine ;  mount  in  damar.  It  is  not  difficult  to 
obtain  preparations  furnishing  a  good  general  view ;  the  vestibular  mem- 
brane is  usually  torn,  so  that  the  ductus  cochlearis  and  scala  vestibuli 
appear  as  a  common  space  (Fig.  274).  The  spiral  organ  leaves  most  to 


392  HISTOLOGY. 

be  desired  ;  only  very  thin  sections  which  pass  through  the  organ  verti- 
cally furnish  intelligible  pictures  ;  usually  a  section  contains  several  inner 
and  outer  pillar-cells,  in  part  only  fragments  of  them  ;  the  cells  of  Hen- 
sen  appear  pale  and  swollen  (Fig.  280),  so  that  orientation  presents  many 
difficulties  to  the  beginner. 

Among  animals,  the  cochlea  of  the  guinea-pig  and  of  the  bat  are  to 
be  recommended  ;  it  is  not  embedded  in  spongy  bone  and  does  not  need 
to  be  chiseled  ouc  and  punctured,  but  can  at  once  be  placed  in  the  fixing 
fluid. 

No.  189. — The  Nerves  of  tlie  Macula,  Cristce,  and  Cochlea. — For 
this  purpose  the  ear  of  the  newborn  mouse  is  recommended,  treated  ac- 
cording to  the  method  given  on  page  41.  The  base  of  the  cranium,  after 
removal  of  the  vertex,  brain,  and  lower  jaw,  is  to  be  placed  for  from  three 
to  four  days  in  the  osmio-bichromate  mixture  and  for  two  days  in  the 
silver  solution.  As  a  rule  it  is  necessary  to  employ  the  double  method 
(p.  42).  Cut  horizontal  and  frontal  sections  through  the  cranium  without 
decalcifying  it.  The  former  are  the  more  readily  made. 

No.  190. — The  EustacMan  Tube. — To  obtain  transverse  sections  (in- 
cluding cartilage  and  mucosa)  the  oblique  direction  of  the  tube  down- 
ward, forward,  and  inward  must  be  ascertained.  Cut  out  the  pharyngeal 
division  of  the  tube  together  with  the  surrounding  muscles  and  fix  it  in 
2OO  or  300  c.c.  of  Miiller's  fluid  (p.  31).  In  from  three  to  six  weeks 
wash  it  in  running  water  and  harden  it  in  100  c.c.  of  gradually-strength- 
ened alcohol  (p.  33).  The  sections  may  be  stained  in  Hansen's  hema- 
toxylin  (p.  36)  and  mounted  in  damar  (p.  45).  For  a  general  view, 
examine  with  the  low  power. 

No.  191. — The  Ceruminous  Glands. — Cut  out  the  ear  with  the  car- 
tilaginous auditory  passage  close  to  the  bony  auditory  passage.  From 
the  cartilaginous  portion  cut  a  piece  I  cm.  square  and  place  it  in  30  c.c. 
of  absolute  alcohol.  The  tissue  may  be  sectioned  on  the  following  day. 
If  it  is  desired  to  see  the  coil  and  the  excretory  duct  the  sections  must 
be  tolerably  thick  ( — 0.5  mm.).  Nuclear  staining  with  Hansen's  hema- 
toxylin  (p.  36)  may  be  employed  (Fig.  283).  Examine  thin  unstained 
sections  in  diluted  glycerol ;  in  these  the  fat-globules  and  pigment-gran- 
ules can  be  seen.  The  organs  of  newborn  children  are  especially  suit- 
able for  this  purpose.  In  adults  the  tubules  are  widely  dilated  and  do 
not  furnish  good  general  views.  On  the  other  hand,  the  cuticular  border 
of  the  gland-cells  is  distinct  in  the  adult,  which  in  the  newborn  I  miss 
(compare  with  Fig.  284). 


XIII.— THE   OLFACTORY   ORGAN. 

In  this  chapter  the  entire  nasal  mucous  membrane  will  be  described. 
The  olfactory  mucous  membrane  proper  in  man  is  confined  to  the  middle 
of  the  superior  turbinal  bone  and  to  the  corresponding  portions  of  the 
nasal  septum  ;  the  remaining  portions  of  the  nasal  fossae  (the  accessory 
nasal  spaces  included)  are  covered  with  respiratory  mucous  membrane. 
In  addition  there  is  another  division  in  the  region  of  the  movable  nose 
(vestibulum  nasi)  which  is  clothed  by  a  continuation  of  the  skin.  Accord- 
ingly three  different  divisions  of  the  nasal  mucous  membrane  are  to  be 
distinguished. 

THE    VESTIBULAR    REGION. 

The  mucous  membrane  of  the  vestibular  region  consists  of  a  strati- 
fied squamous  epithelium  and  a  tunica  propria  supporting  papillae. 
Numerous  sebaceous  glands  and  the  hair-follicles  of  the  stiff  nasal  hairs 
(vibrissae)  are  embedded  in  the  tunica  propria. 

THE    RESPIRATORY   REGION. 

The  respiratory  portion  of  the  nasal  mucous  membrane  consists  of 
a  stratified  ciliated  columnar  epithelium  (Fig.  n),  that  sometimes  con- 

Epithelium. 


Glands.   — ^?3^W 

I 

Tunica  propria. 


Artery. 

Periosteum  of  the  vomer. 


FIG.  285.— THICK  VERTICAL  SECTION  OF  RESPIRATORY  Mucous  MKMBRANE  OF  THE  HUMAN  NASAL 
SEPTUM.  X  20.  The  excretory  ducts  of  two  glands  are  visible,  t.  Funnel-shaped  depression ; 
v,  vein.  Techn.  No.  193. 

tains  many,   sometimes  few  goblet-cells,   and   of  a   conspicuous  tunica 
propria,  up  to  four  millimeters  thick  on  the  inferior  turbinal  bone,  which 

393 


394 


HISTOLOGY. 


is  built  of  fibrillar  connective  tissue,  of  a  large,  variable  number  of  leu- 
cocytes, and  toward  the  epithelial  border  is  condensed  to  a  homogeneous 
membrana  propria  provided  with  minute  apertures.  These  leucocytes  are 
occasionally  balled  together  in  solitary  nodules  and  often  wander  in  large 
numbers  through  the  epithelium  into  the  nasal  fossae  (cf.  p.  221). 

The  tunica  propria  in  man  contains  branched  tubular  glands,  which 
produce  partly  mucous  and  partly  serous  secretion,  therefore  are  mixed 
glands.  Not  infrequently  they  open  in  funnel-shaped  depressions  (Fig. 
285,  /),  which  are  lined  by  an  extension  of  the  superficial  epithelium  and 
on  the  inferior  turbinal  are  perceptible  by  the  unaided  eye.  In  the  acces- 
sory nasal  spaces  the  epithelium  and  tunica  propria  are  considerably 
thinner  ( — 0.02  mm.),  but  otherwise  of  the  same  structure  ;  the  glands 
are  small  and  few  in  number. 


THE   OLFACTORY    REGION. 

The  mucous  membrane  of  this  region  by  its  yellowish-brown  color 
can  be  macroscopically  distinguished  from  the  rosy  mucosa  of  the  res- 
piratory division.  It  consists  of  an  epithelium,  the  olfactory  epithelium, 
and  of  a  tunica  propria.  In  the  olfactory  epithelium  two  forms  of  cells 
occur.  The  one  form  (Fig.  286,  st)  is  cylindrical  in  its  upper  half  and 

here  contains  a  yellowish  pigment  and 
minute  granules,  often  arranged  in  longi- 
tudinal rows.  The  lower  half  is  slen- 
derer, the  edge  is  serrated  and  indented, 
the  inferior  end  is  forked  and  is  said  to 
unite  with  the  similar  ends  of  neighbor- 
ing cells  to  form  a  protoplasmic  network. 
These  elements  are  called  sustcntacular 
cells.  Their  usually  oval  nuclei  lie  at  the 
same  level  and  in  vertical  sections  occupy 
a  narrow  belt,  the  zone  of  the  oval  nuclei 
(Fig.  288).  The  second  form  (Fig.  286,;- 
and  Fig.  287)  possesses  a  spherical  nu- 
cleus and  only  in  the  vicinity  of  the  latter 

an  appreciable  amount  of  protoplasm  ;  from  this  a  slender  ciliated  cylin- 
drical process  extends  upward,  while  from  the  opposite  pole  a  very  deli- 
cate process  continues  directly  into  the  axis-cylinder  of  a  nerve-fiber. 
These  cells,  the  olfactory  cells,  are  ganglion-cells  and  their  lower  process 
a  centripetal  nerve-fiber.  Their  round  nucleolated  nuclei  lie  at  different 
levels  and  occupy  a  broad  belt,  the  zone  of  the  round  nuclei  (Fig.  288,  zr\ 


FIG.  286.— ISOLATED  CELLS  OF  THE  OL- 
FACTORY MUCOSA  OF  A  RABBIT.  X  560. 
st.  Sustentacular  cells ;  s,  extruded  mu- 
cus resembling  cilia  ;  r,  olfactory  cells,  at 
r1  the  lower  process  has  been  torn  off; 
y,  ciliated  cells;  b,  cells  of  olfactory 
glands.  Techn.  No.  192. 


THE    OLFACTORY    ORGAN. 


395 


Occasionally,  in  the  nonnucleated  epithelial  territory,  round  nuclei  in 
varying  number  are  found  above  the  zone  of  the  oval  nuclei ;  they  either 
belong  to  dislocated  olfactory  cells  or  are  the  nuclei  of  wandering,  often 
pigment*ed,  leucocytes.  In  addition  to  these  two  kinds  of  cells  there  are 
intermediate  forms,  that  sometimes  resemble  the  olfactory  elements, 
sometimes  the  sustentacular  cells.  At  the  border  of  the  epithelium, 
toward  the  connective  tissue,  there  is  a  protoplasmic  network  furnished 
with  nuclei,  the  so-called  basal  cells  (Fig.  289,  b).  The  surface  of  the 
epithelium  is  covered  by  an  extremely  delicate  homogeneous  membrane, 
the  mcmbrana  liinitans  olfactoria  ;  it  is  pierced  by  the  ciliated  extremities 
of  the  olfactory  cells  and  is  itself  covered  by  a  peculiar  substance,  re- 
garded by  some  authors  as  a  cuticular  formation  similar  to  that  of  the 
intestinal  epithelium,  by  others  as  delicate  cilia,  by  still  others  interpreted 
as  minute  particles  of  discharged  mucus  (Fig.  286,  s). 


•  Epithelium. 


Tunica  propria. 


Bundles  of  fibers  of  olfactory  nerve. 


Centripetal  process  of  an  olfactory  cell. 


FIG.  287. — VERTICAL  SECTION  THROUGH  THE  OLFACTORY  REGION  OF  A  YOUNG  RAT.    X  480. 

Techn.  No.  195. 

The  tunica  propria  consists  of  a  loose  feltwork  .of  rigid  connective- 
tissue  fibers  intermingled  with  delicate  elastic  fibers,  which  in  some 
animals  toward  the  epithelium  (for  example,  in  the  cat)  is  condensed 
to  a  structureless  membrane.  Numerous  glands,  the  so-called  olfac- 
tory glands  (Bowman),  are  embedded  in  the  tunica  propria ;  they  are 
either  simple  or  (for  example,  in  man)  branched  follicles,  in  which 
an  excretory  duct  situated  in  the  epithelium,  a  body,  and  a  fundus 
may  be  distinguished  (Fig.  288,  a).  The  cells  of  the  body  of  the 
glands  are  pigmented.  The  olfactory  glands  (also  those  of  man)  until 
recently  were  regarded  as  serous  glands,  but  latterly  they  have  been 
pronounced  mucous  glands.  The  olfactory  glands  frequently  advance 
beyond  the  territory  of  the  olfactory  mucous  membrane  and  are  found  in 
the  adjoining  portions  of  the  respiratory  mucous  membrane.  The  tunica 


396 


HISTOLOGY. 


propria  also  carries  the  ramifications  of  the  nerves.     The  branches  of  the 
olfactory  nerve  are  accompanied  by  processes  of  the  dura  and  consist 


Epithelium. 


Tunica  propria. 


FIG.  288.— VERTICAL  SECTION  OK  THE  OLFACTORY  MUCOSA  OF  A  RABBIT.  X  50.  zo,  Zone  of  oval,  zr, 
zone  of  round  nuclei,  dr.  Olfactory  glands;  a,  excretory  duct,  k,  body,  g,  fundus.  n,  Branches  of 
olfactory  nerve  cut  transversely;  v,  veins;  ar,  arteries;  f>,  bundles  of  connective  tissue  in  cross- 
section.  Techn.  No.  194. 

throughout  of  nonmedullated  fibers,  that  readily  separate  into  their  com- 
ponent fibrillae  ;  the  fibers  grouped  into  bundles  are  the  inferior  processes 
of  the  olfactory  cells,  which  pass  in  horizontal  arches  from  the  epithe- 


Epithelium. 


?,Afc&i 


Tunica  propria. 


FIG.  289.— VERTICAL  SECTION  THROUGH  THE  OLFACTORY  MUCOSA  OF  A  RABBIT.  X  560.  s,  Cuticular 
border;  zo,  zone  of  oval,  zr,  zone  of  round  nuclei ;  b,  basal  cells  ;  dr,  portions  of  olfactory  glands, 
on  the  right  the  lower  portion  of  the  excretory  duct  is  shown ;  n,  branch  of  the  olfactory  nerve. 
Techn.  No.  194. 

Hum  and  descend  into  the  tunica  propria  and  by  union  with  neighboring 
bundles  form  the  branches  of  the  olfactory  nerve.  The  terminal  rami- 
fications of  the  fifth  nerve  lie  within  the  tunica  propria ;  delicate  fibers 


THE    OLFACTORY    ORGAN.  397 

that  ascend  to  the  epithelium  and  there  terminate  in  free  ends  possibly 
belong  to  the  fifth  nerve.* 

Of  the  blood-vessels  of  the  nasal  mucosa  the  arterial  stems  run  in  the 
deeper  strata  of  the  tunica  propria  (Fig.  285,  Fig.  288) ;  they  supply  a 
capillary  network  that  reaches  close  beneath  the  epithelium.  The  veins 
are  remarkable  for  their  size  (Fig.  285)  and  over  the  posterior  end  of  the 
inferior  turbinal  bone  form  so  dense  a  network  that  the  tunica  propria 
resembles  cavernous  tissue. 

The  lymph-vessels  form  a  coarse-meshed  net  lying  in  the  deeper 
strata  of  the  tunica  propria.  The  lymph-vessels  of  the  olfactory  mucosa 
may  be  injected  from  the  subarachnoidal  space,  through  the  perineurial 
sheaths  of  the  branches  of  the  olfactory  nerve  acquired  from  the  cere- 
bral membranes  on  passing  through  the  cribriform  plate. 

Medullated  twigs  of  the  fifth  nerve  may  be  found  in  the  respiratory 
as  well  as  in  the  olfactory  mucosa. 

TECHNIC. 

No.  192. — Olfactory  Cells. — Saw  open  the  head  of  a  rabbit  in  the 
median  line.  The  olfactory  mucosa  is  easily  recognized  by  its  brown 
color.  With  fine  scissors  cut  out  a  small  piece  of  the  mucosa,  about  5 
mm.  long,  together  with  the  corresponding  portion  of  the  turbinal  bone, 
and  place  it  in  20  c.c.  of  one-third  alcohol  (p.  20).  In  five  or  seven  hours 
transfer  the  same  to  5  c.c.  of  picrocarmine  and  on  the  following  day  to 
10  c.c.  of  distilled  water.  In  about  ten  minutes  remove  the  piece  and 
lightly  strike  it  against  a  slide  on  which  a  drop  of  diluted  glycerol  has 
been  placed  ;  stirring  with  the  needle  is  to  be  avoided.  Carefully  apply 
a  cover-glass.  In  addition  to  many  fragments  of  cells  many  well-pre- 
served sustentacular  elements  may  be  obtained.  Very  frequently  the 
delicate  central  process  of  the  olfactory  cells  is  wanting  (Fig.  286). 

No.  193. — The  Mucous  Membrane  of  the  Respiratory  Region. — Cut 
out  a  piece  about  5  or  10  mm.  long  from  the  lower  half  of  the  nasal 
septum  ;  strip  off  the  mucosa  and  fix  and  harden  it  in  about  20  c.c.  of 
absolute  alcohol  (p.  30).  Use  the  nasal  mucous  membrane  of  the  rab- 
bit's head  (No.  192)  for  thin  sections;  embed  the  pieces  in  liver  and 
stain  sections  with  Hansen's  hematoxylin  ;  mount  in  damar.  For  gen- 
eral views  the  mucous  membrane  of  human  cadavers  answers,  which  is 
to  be  treated  in  the  same  manner ;  thick,  unstained  sections  are  to  be 
mounted  in  diluted  glycerol  (Fig.  285). 

No.  1 94. — The  Mucous  Membrane  of  the  Olfactory  Region. — Remove 

*  Different  authors  have  described  structures  in  the  nasal  mucous  membrane  resembling 
the  taste-buds.  It,  however,  is  not  certain  but  that  folds  of  the  nasal  mucous  membrane  have 
been  mistaken  for  these  "  olfactory-buds." 


39$  HISTOLOGY. 

pieces  from  3  to  6  mm.  long  of  the  brown  mucosa  from  the  upper  por- 
tion of  the  nasal  septum  of  a  rabbit  (No.  192),  and  place  them  for  three 
hours  in  20  c.c.  of  Ranvier's  alcohol,  which  somewhat  loosens  the  ele- 
ments of  the  olfactory  epithelium.  Transfer  the  pieces  carefully  to  3  c.c. 
of  2  per  cent,  osmium  solution  plus  3  c.c.  of  distilled  water,  and  place 
the  whole  for  from  fifteen  to  twenty-four  hours  in  the  dark.  At  the 
expiration  of  this  time  the  pieces  are  to  be  placed  for  a  half-hour  in 
20  c.c.  of  distilled  water  and  then  hardened  in  30  c.c.  of  gradually- 
strengthened  alcohol.  The  hardened  pieces  are  to  be  embedded  in  liver 
and  sectioned.  Stain  the  sections  from  twenty  to  thirty  seconds  in  Han- 
sen's  hematoxylin  ;  mount  them  in  damar. 

In  order  to  obtain  good  views  of  the  glands  make  thick  sections 
transverse  to  the  course  of  the  nerve-fibers  (Fig.  288).  For  the  exhibi- 
tion of  the  nerve-fibers  and  the  epithelium  thin  sections  parallel  to  the 
course  of  the  fibers  are  suitable  (Fig.  289). 

No.  195. — The  nerve-processes  of  the  olfactory  cells  may  be  obtained 
in  preparations  made  according  to  Techn.  No.  179.      In  these  the  duct 
system  of  the  olfactory  glands  often  is  blackened. 


XIV.  THE  TASTE-BUDS. 

The  taste-buds,  the  gustatory  organs,  are  oval  bodies,  about  80  [i 
long  and  40/2  broad,  which  are  completely  embedded  in  the  epithelium 
of  the  oral  mucous  membrane  ;  their  base  rests  upon  the  tunica  propria, 
the  upper  end  reaches  to  the  surface  of  the  epithelium,  which  here  ex- 
hibits a  funnel-shaped  depression,  the  taste-pore.  Each  taste -bud  con- 
sists of  two  kinds  of  elongated  epithelial-cells  ;  the  one  is  either  every- 
where of  the  same  diameter  or  tapers  at  the  basal  end,  which  occasion- 


r   /^--    ,    •'  /^       -     '•-      • 

^mi 
*- 


Epithelium. 


Tunica  propria. 


FIG.  200.— VERTICAL  SECTION  OK  Two  RIDGES  OF  THE  PAPILLA  FOLIATA  OF  A  RABBIT.  X  80.  Each 
ridge,  /,  bears  secondary  ridges,  t;  g,  taste-buds;  «,  medullated  nerves;  rf,  serous  gland  ;  a,  por- 
tion of  an  excretory  duct  of  a  serous  gland  ;  M,  muscle-fibers  of  the  tongue.  Techn.  No.  197. 

ally  is  forked,  while  the  upper  end  is  prolonged  to  a  fine  point ;  the 
protoplasm  is  clear.  These  cells  constitute  the  bulk  of  the  taste-bud, 
are  principally  situated  at  the  periphery  of  the  bud,  and  are  called  teg- 
mental  cells.  They  serve  as  support  and  sheath  for  the  gustatory  cells, 
which  are  the  real  percipient  epithelial  elements.  The  gustatory  cells 
are  small  and  only  slightly  thickened  where  the  nucleus  is  situated ;  the 
latter  is  sometimes  nearer  the  lower  end,  sometimes  in  the  middle, 
rarely  at  the  upper  end  of  the  cell.  The  upper  division  of  the  cell  is 
cylindrical,  or  more  frequently  conical,  and  bears  on  its  free  end  a  stiff, 

399 


400 


HISTOLOGY. 


refractile,  hair-like  process,  a  cuticular  formation  (Fig.  291);  the  lower 
division  is  sometimes  slender,  sometimes  thick,  and  terminates  in  a 
blunted  end  or  in  a  triangular  foot,  without  however  extending  into 


Taste-pore. 
Hair-process." 


Taste-bud.    -%*% 


Epithelium. 


iTunica  propria. 
FIG.  291. — FROM  A  VERTICAL  SECTION  OF  THE  PAPILLA  FOLIATA  OF  A  RABBIT.    X  560.    Techn.  No.  197. 

the  connective  tissue  of  the  mucosa.  Their  protoplasm  is  granular. 
Not  infrequently  many  leucocytes  are  found  in  the  interior  of  the  taste- 
bud. 

The  taste-buds  chiefly  occur  in  the  lateral  walls  of  the  circumvallate 


Taste-bud. 


Intragemmal  fibers. 


Secondary  ridge. 


Epithelium 


Secondary  ridge. 


Connective  tissue. 


Nerve. 


FIG.  292.— FROM  A  VERTICAL  SECTION  OF  THE  FOLIATE  PAPILLA  OF  A  RABBIT.    X  220.    At  x  the  inter- 
gemmal  fibers  lie  upon  a  taste-bud.    For  orientation  compare  with  Fig.  290.  Techn.  No.  199. 

papillae  and  on  the  ridges  of  the  papillae  foliatae,  in  smaller  number  on 
the  fungiform  papillae,  on  the  soft  palate,  and  on  the  posterior  surface  of 
the  epiglottis. 


THE    TASTE-BUDS.  40  I 

The  conjecture  that  the  terminal  ramifications  of  the  glossopharyn- 
geal  nerve  have  the  same  anatomic  relation  to  the  gustatory  cells  that 
the  olfactory  nerve-fibers  have  to  the  olfactory  cells  has  been  shown  to 
bs  erroneous.  The  terminal  branches  of  the  glossopharyngeal  nerve 
consist  of  medullated  and  gray  nerve-fibers  beset  with  microscopic  (sym- 
pathetic) ganglia,*  which  form  a  dense  plexus  in  the  tunica  propria, 
from  which  numerous  branches  arise.  Some  of  the  latter  perhaps  termi- 
nate in  the  connective  tissue  in  end-bulbs,  but  the  majority  of  the  gray 
fibers  penetrate  into  the  epithelium.  Here  two  kinds  of  fibers  may  be 
distinguished.  The  one  kind,  the  "  intragemmal  "  fibers,  enter  the  taste- 
buds,  divide,  and  form  a  plexus  beset  with  numerous  conspicuous  vari- 
cosities  that  extends  up  to  the  taste-pore  ;  these  fibers  do  not  anastomose 
with  one  another,  nor  do  they  connect  with  the  gustatory  cells,  but  all 
terminate  in  free  ends.  The  other,  the  smoother  "  intergemmal  "  fibers, 
penetrate  the  epithelial  areas  between  the  taste-buds  and,  usually  with- 
out dividing,  extend  to  the  uppermost  strata  of  the  epithelium. 

• 

TECHN1C. 

No.  196. — For  orientation  witJi  regard  to  the  number  and  position  of 
the  taste-buds  proceed  according  to  the  method  in  No.  96.  Suitable 
objects  are  the  circumvallate  papillae  of  any  animal  and  the  papillae  foliatae 
of  the  rabbit.  The  latter  consist  of  elevated  groups  of  parallel  folds  of 
the  mucosa,  found  one  on  either  edge  of  the  root  of  the  tongue.  In 
moderately  thin  sections  vertical  to  the  long  axis  of  the  folds,  with  the 
low  power,  the  taste -buds  may  be  recognized  as  clear  spots. 

No.  197. —  The  Structure  of  tJie  Taste-buds. — Dissect  off  with  scis- 
sors a  papilla  foliata  of  a  rabbit,  with  as  little  as  possible  of  the  subjacent 
muscle  substance.  Pin  the  piece  with  spines  on  a  cork-stopper,  the 
muscle  side  toward  the  cork,  and  expose  it  for  one  hour  to  the  vapor  of 
osmicacid  (see  further  p.  32,  7).  Thin  sections  of  the  hardened  prepara- 
tion embedded  in  liver  are  to  be  stained  thirty  seconds  in  Hansen's  hema- 
toxylin  and  mounted  in  damar  (Fig.  290). 

No.  198. — Exhibition  of  the  Nerves. — With  scissors  cut  out  a  cir- 
cumvallate papilla  (without  the  wall),  and  place  it  for  ten  minutes  in  the 
filtered  juice  of  a  lemon  ;  then  transfer  it  to  5  c.c.  of  a  I  per  cent,  gold- 
chlorid  solution  and  place  the  whole  for  one  hour  in  the  dark.  Lift  the 
papilla  with  wooden  rods  from  the  gold-chlorid  solution  into  a  watch- 
glass  with  distilled  water  and  wash  it  by  moving  it  to  and  fro.  Transfer 
it  to  20  c.c.  of  distilled  water  to  which  three  drops  of  acetic  acid  have 
been  added.  In  this  expose  the  papilla  to  daylight  until  the  reduction  is 

*  Whether  the  so-called  "  taste  granules  "  beneath  the  epithelium  of  the  papillae  foliatae 
are  multipolar  nerve-c;lls  is  very  questionable  ;  a  nerve-process  has  not  as  yet  been  demonstrated. 
26 


402  HISTOLOGY. 

completed,  which  usually  requires  three  days.  Harden  the  papilla  in 
the  dark  ,in  30  c.c.  of  gradually-strengthened  alcohol.  Embed  the  object 
and  make  the  thinnest  possible  sections.  Mount  in  damar.  The  nerve- 
fibers  are  dark-red  to  black  ;  the  gustatory  cells  are  also  dark  (compare 
with  Fig.  292).  The  foliate  papillae  of  the  rabbit  are  not  suitable  for  this 
method. 

No.  199. — Place  the  papillae  foliatae  of  a  rabbit  for  three  days  in 
the  osmio-bichromate  mixture,  for  two  days  in  the  silver  solution  (p.  41). 
The  double  method  is  recommended.  The  intergemmal  fibers  are  more 
numerous  and  more  readily  blackened  than  the  intragemmal  fibers,  which 
are  exceedingly  delicate  (Fig.  292).  Frequently  single  cortical  and  gus- 
tatory cells  become  blackened. 


APPENDIX. 

MICROTOME  TECHNIC. 


THE   MICROTOME. 

The  most  useful  microtomes  are  constructed  according  to  two  dif- 
ferent principles. 

The  principle  of  the  one  kind  consists  therein,  that  the  object  to  be 
sectioned  is  elevated  by  the  shifting  of  the  object-holder  up  an  inclined 
plane. 

In- the  other  form,  the  object  is  elevated  in  a  vertical  direction  by  a 
micrometer-screw. 

Both  kinds  are  excellent  instruments.* 

All  parts  of  the  microtome  should  be  kept  as  clean  as  possible. 
When  not  in  use  it  should  be  protected  from  dust  by  covering  it  with  a 
light  wooden  case.  The  slideway  in  which  the  knife  moves  must  be  kept 
scrupulously  clean.  It  should  be  occasionally  cleansed  with  a  cloth 
moistened  in  benzin  and  should  then  be  freely  lubricated  with  vaselin,  so 
that  the  sliding-block  will  pass  evenly  throughout  the  entire  slideway  at 
the  lightest  touch.  Especial  care  must  be  bestowed  upon  the  knife. 
Only  with  a  very  sharp  knife  can  very  thin  sections  be  made  or  ribbon- 
cutting  be  done.  A  really  sharp  knife  should  easily  pass  through  a 
thin  hair  held  at  one  end  between  the  fingers. 

*  The  workmanship  of  the  sliding  microtomes  of  Thoma,  made  by  Jung  in  Heidelberg,  is 
exquisite,  as  I  know  from  my  own  experience.  The  size  No.  IV  is  especially  to  be  recom- 
mended. For  several  years  I  have  used  the  microtome  of  Schanze  in  Leipzig,  Model  B,  No.  9, 
the  construction  of  which  leaves  nothing  further  to  be  desired.  The  microtomes  constructed  on 
the  same  principle,  by  G.  Mihe  in  Hildesheim,  are  also  to  be  highly  recommended,  and  very 
good  are  those  of  A.  Becker  in  Gottingen. 

Editor's  remark  :  The  automatic  microtome  of  Minot  is  widely  used,  particularly  in 
American  laboratories.  This  instrument  is  distinguished  from  those  above  described  by  the 
great  rapidity  with  which  it  can  be  worked.  Therefore  it  is  to  be  highly  recommended,  espe- 
cially for  the  preparation  of  long  series  of  paraffin-sections  attached  one  to  the  other  in  the  form 
of  a  ribbon  ("ribbon-cutting").  In  exactness  of  action  it  is  hardly  surpassed  by  the  German 
models,  from  which  it  altogether  differs  in  construction.  The  object  is  moved  by  the  rotation 
of  a  wheel  in  a  vertical  direction  up  and  down  across  the  edge  of  a  knife  and  previous  to  every 
cut  is  advanced  toward  the  knife  a  certain  distance,  which  is  regulated  by  an  automatic  microm- 
eter-screw. 

It  is  difficult  to  recommend  in  particular  any  one  of  the  microtomes  mentioned.  Each  has 
its  advantages  and  disadvantages,  and  to  be  successfully  used  demands  a  certain  amount  of  ex- 
perience and  practice,  which  determines  the  individual  preference  for  a  certain  instrument. 

The  Minot-microtome  is  made  by  E.  Zimmermann,  T^ipzig,  Germany,  and  in  the  United 
States  by  the  Bausch  &  Lomb  Optical  Co.,  New  York  and  Rochester,  N.  Y.  The  latter  also 
make  a  very  satisfactory  sliding  microtome,  on  the  principle  of  the  Schanze-microtome. 

403 


404  HISTOLOGY. 


EMBEDDING. 

THE  PARAFFIN  METHOD. 

The  following  materials  and  apparatus  are  required  : — 

1.  Paraffin:  two  kinds,  a  soft  (melting  point  45°   Celsius)   and  a 
hard  (melting  point   52°    Celsius).      Of  this  prepare   a  mixture  which 
melts  at  50°  Celsius.     On    the  proper  proportions  of  the  two  sorts   of 
paraffin  in   the   mixture   much   depends  ;   many  a  failure   is    due  to  an 
unsatisfactory  mixture.     The   precise   proportions  cannot  be  given  be- 
cause the  consistence  of  the  paraffin  depends  in  a  great  measure  on  the 
outer  temperature.     Then,  too,  hard   objects,  as  well  as  the   cutting  of 
very  thin  sections,  require  a  harder  mixture  than  usual.      For  winter,  at 
a  room-temperature  of  20°  Celsius,  a  mixture  of  30  grams  of  soft  and  25 
grams  of  hard  paraffin*  answers  for  most  purposes. 

2.  Chloroform  :  20  c.c. 

3.  Paraffin-chloroform  :  a  saturated  solution  (5  grams  of  the  paraffin 
mixture  and  25  c.c.  of  chloroform).     This   solution  is   liquid  at  room- 
temperature. 

4.  An  embedding  oven  of  block-tin  with  double  walls,  between  which 
is  a  space  to  be  filled  with  water. f     A  small  gas-burner  is  to  be  placed 
beneath  the  oven.     On  top  there  are  three  openings  ;  two  lead  into  the 
space  between  the  walls,  into  one  a  Reichert  thermo-regulator  {  is  to  be 
inserted,  into  the  other  a  thermometer  ;  the  third  opening  leads  into  the 
air-space  or  oven  and  into  this  a  second   thermometer  is  to  be  inserted. 
The  front  wall  consists  of  a  glass  plate  which   slides   up   and  down   in 
grooves.     The  interior  of  the  oven  is  divided  into  three   compartments 
by  means  of  two  adjustable  shelves.     The  oven  should  be  25  cm.  long, 
15  cm.  high,  and  15  cm.    deep.     The  embedding   oven  with   its   acces- 
sories is  indispensable  if  much  embedding  in  paraffin  is  to  be  done  ;   but 
the  paraffin  may  be  melted  on  a  water-bath  and  kept  liquid  with  a  small 
spirit-flame. 

5.  An   Embedding  Frame. — This   consists   of  two   adjustable   bent 
metal  frames,  placed  together 

this  way. 


Instead  of  this  frame  little  paper  trays  made   of  stiff  paper  or  cardboard 
can  be  used. 

The  objects  to  be  embedded  must  be  absolutely  free  from  water 
and  to  this  end  should  have  lain  three  days  in  absolute  alcohol  which 
has,  been  changed  several  times;  they  are  then  to  be  transferred  to  a 
bottle  containing  20  c.c.  of  chloroform,  in  which  they  should  remain 

*  To  be  obtained  of  Dr.  Grubler,  of  Leipzig. 

fMade  by  R.  Jung,  Heidelberg,  Germany,  and  in  the  United  States  by  the  Bausch  & 
Lomb  Optical  Co.,  New  York. 

J  To  be  obtained  of  the  Bausch  &.  Lomb  Optical  Co.,  New  York. 


MICROTOME    TECHNIC.  405 

until  the  following  day.  From  this  the  objects  should  be  carried  to  the 
solution  of  paraffin  in  chloroform  and  in  from  two  to  eight  hours,  accord- 
ing to  their  size,  transferred  to  a  capsule  containing  melted  (but  not  too 
hot)  paraffin.  In  about  a  half  hour  the  objects  are  to  be  transferred  to  a 
second  capsule  with  melted  paraffin,*  where,  according  to  their  size,  they 
are  to  remain  from  one  to  five  hours. f  The  paraffin  should  not  be 
heated  more  than  two  or  three  degrees  above  its  melting  point  ;  for  the 
mixture  advised  the  air  in  the  oven  should  have  a  temperature  of  50° 
Celsius. 

When  the  objects  have  been  in  the  paraffin  bath  the  required  length 
of  time,  place  a  slide  in  a  broad  dish  and  on  this  the  embedding  frame, 
into  which  paraffin  and  object  now  are  to  be  poured.  Then,  while 
the  paraffin  is  still  fluid,  with  a  heated  needle  place  the  object  in  the 
desired  position  ;  so  soon  as  this  is  done  carefully  pour  cold  water  into 
the  dish  until  it  reaches  the  upper  margin  of  the  frame  ;  the  paraffin  will 
at  once  begin  to  harden,  whereupon  more  water  may  be  added  until  the 
entire  frame  is  submerged.  By  this  manipulation  the  paraffin  hardens 
into  a  homogeneous  mass,  whereas  otherwise  it  is  apt  to  crystallize  and  is 
then  difficult  to  cut  and  also  has  an  injurious  influence  on  the  structure 
of  the  embedded  tissues.  In  about  ten  minutes  the  metal  frames  may 
be  removed  ;  the  paraffin  block  should  be  allowed  to  remain  in  the  water 
on  the  slide  until  it  is  completely  hard. 

The  embedded  object  may  be  sectioned  in  a  half  hour.  In  case  it 
is  to  be  used  later  mark  it  with  a  needle.  In  the  paraffin  the  object  can 
be  kept  for  an  indefinite  period. 

THE  CELLOIDIN  METHOD. 

Two  solutions  are  required  : — 

a.  A  thin  solution  of  about  30  grams  of  celloidin  cut  into  cubes  dis- 
solved in  60  c.c.  of  a  mixture   of  equal  parts   of  absolute   alcohol  and 
ether. 

b.  A  somewhat  thicker  solution  of  30  grams  of  celloidin  dissolved 
in  40  c.c.  of  a  mixture  of  equal  parts  of  absolute  alcohol  and  ether.     This 
solution  has  the  consistence  of  a  thick  syrup. 

Both  solutions  should  be  kept  in  wide-mouthed  bottles.  If  they 
become  too  thick  they  may  be  thinned  by  the  addition  of  some  of  the 
alcohol-ether  mixture.  After  a  time  the  solutions  become  turbid  and 
milky  ;  it  is  better  then  to  let  them  dry  completely  and  to  redissolve  the 
pieces  in  the  alcohol-ether  mixture. 

The  tissues  to  be  embedded  must  be  completely  free  from  water  and 
must  have  lain  one  or  two  days  in  absolute  alcohol  which  has  been 
changed  several  times.  From  this  the  objects  should  be  transferred  to 
the  thin  and  on  the  following  day  to  the  thick  celloidin  solution.  In  the 
latter,  the  objects  may  remain  for  an  indefinite  length  of  time.  Usually 

*  If  the  paraffin  has  been  melted  on  a  water-bath,  place  the  flame  at  such  a  distance  that 
the  surface  of  the  paraffin  remains  covered  by  a  thin  film. 

f  This  is  sufficient  for  all  cases  ;  for  small  objects  from  one  to  two  hours  will  be  enough. 


406  HISTOLOGY. 

they  are  sufficiently  permeated  after  twenty -four  hours,  but  large  objects 
enclosing  many  spaces  must  remain  in  the  thick  solution  about  eight 
days.  The  object  should  then  be  quickly  placed  on  a  cork-stopper  and 
some  celloidin  poured  over  it.  In  doing  this  care  must  be  taken  not  to 
press  the  object  against  the  cork,  lest  it  become  detached.  There  should 
be  a  stratum  of  celloidin  one  or  two  millimeters  thick  between  the  cork 
and  the  object.*  Now  the  whole  is  to  be  placed  under  a  bell-glass  to 
slowly  dry  ;  the  bell-glass  should  not  be  air-tight,  and  to  avoid  this 
should  be  supported  on  one  side  on  a  needle  or  something,  similar. 
Delicate  objects  dry  in  a  half  hour,  larger  objects  in  four  hours  ;  they 
are  then  to  be  placed  in  a  glass  jar  with  30  c.c.  of  80  per  cent,  alcohol. 
In  order  that  the  objects  may  be  submerged,  glue  the  under  surface  of 
the  cork-stopper  by  means  of  celloidin  to  the  inner  surface  of  the  lid  of 
the  jar.  On  the  following  day  the  alcohol  should  be  replaced  by  70 
per  cent,  alcohol,  in  which  the  tissue  may  remain  an  indefinite  length  of 
time. 

In  order  to  cut  thin  sections  the  celloidin  must  be  hardened  ;  for 
this  purpose  transfer  the  objects  embedded  in  celloidin  from  the  80  per 
cent,  alcohol  for  two  days  or  longer  into  an  alcohol-glycerol  mixture 
(80  per  cent,  alcohol  one  part,  pure  concentrated  glycerol  from  six  to 
ten  parts).  The  larger  the  proportion  of  glycerol  to  alcohol,  the  harder 
the  celloidin  becomes.  This .  mixture  may  be  differently  prepared  ;  an 
extreme  limit  is  one  part  of  alcohol  to  30  parts  of  glycerol.  Still  greater 
difference  in  the  proportions  produces  strong  curling  of  the  sections.  In 
order  to  prevent  the  yielding  of  the  elastic  celloidin  block,  dry  it  care- 
fully with  filter-paper  when  it  is  removed  from  the  alcohol-glycerol  mixt- 
ure, make  a  pair  of  lateral  incisions  and  dip  it  into  liquid  paraffin  ;  such 
blocks  cannot  be  preserved  dry,  they  must  be  returned  to  the  alcohol- 
glycerol  mixture. 

Preparations  fixed  by  Golgi's  method  require  special  treatment,  since 
the  absolute  alcohol  has  an  injurious  influence  if  the  object  remains  in  it 
beyond  one  hour.  When  the  tissue  is  taken  from  the  silver  solution  it 
is  to  be  placed  in  30  c.c.  of  95  per  cent,  alcohol,  fifteen  or  twenty 
minutes,  then  hardened  in  absolute  alcohol  for  fifteen  minutes,  then 
placed  in  the  thin  celloidin  solution  for  five  minutes.  Meanwhile,  in  the 
previously  smoothed  lateral  surface  of  a  broad  piece  of  elder-pith  make 
an  excavation  just  large  enough  to  take  in  the  whole  preparation  ;  insert 
it,  cover  it  with  celloidin  solution,  fit  a  second  piece  of  elder-pith  on  the 
first,  pour  on  more  celloidin,  and  place  the  whole  for  five  minutes  under 
a  bell-glass  to  dry  ;  then  transfer  it  to  80  per  cent,  alcohol  for  five 
minutes,  and  cut  sections  with  a  knife  flooded  with  80  per  cent,  alcohol. 
The  microtome  is  altogether  unnecessary ;  satisfactory  sections  can 
easily  be  cut  free-hand.  If  the  microtome  be  used,  the  thickness  of  the 
sections  should  vary  from  40  to  120  ft.  The  elder-pith  should  be 
trimmed  off  so  that  only  a  small  border  (i  mm.)  surrounds  the  celloidin. 

*  This  stratum  must  not  be  thicker;  even  well-hardened  celloidin  is  elastic,  and  a  thick 
layer  would  cause  the  object  to  give  in  sectioning. 


MICROTOME    TECHNIC.  407 


SECTIONING. 

PARAFFIN  OBJECTS. 

With  tlic  Kn'fc  Placed  Obliquely. — The  paraffin  block  containing  the 
tissue  is  to  be  secured  in  a  hollow  cylinder  coated  with  hard  paraffin  (in 
the  Thoma  microtome)  or  (in  the  microtome  of  Schanze)  to  a  little  plate 
adjoining  the  clamp.  With  the  latter  the  plate  is  simply  warmed  and 
the  paraffin  block  glued  to  it  by  pressure.  In  the  case  of  the  cylinder, 
warm  it  and  also  the  base  of  the  paraffin  block  ;  press  the  latter  lightly 
into  the  cylinder  and  by  means  of  a  heated  needle  inserted  between  them 
establish  a  firm  union.  In  order  quickly  to  cool  the  paraffin  place  the 
cylinder  or  the  plate  for  five  minutes  in  cold  water.  The  projecting  por- 
tion of  the  paraffin  block  containing  the  object  should  then  be  trimmed 
to  a  four-sided  column,  the  base  of  which  is  a  right-angled  parallelogram. 

The  column  must  not  be  taller  than  one  centimeter,  and  the  object 
should  be  covered  by  a  layer  of  paraffin  not  over  one  or  two  millimeters 
thick.  The  cylinder  (or  the  plate)  with  the  object  should  now  be  placed 
in  the  microtome.  Sections  are  to  be  cut  with  the  blade  of  the  knife 
dry.  The  position  of  the  knife  depends  on  the  nature  of  the  object. 

Sectioning  with  the  Knife  Placed  Obliquely. — If  the  object  is  large 
and  of  unequal  resistance  the  knife  should  be  so  clamped  that  it  forms  a 
very  acute  angle  with  the  long  axis  of  the  microtome.  The  paraffin 
block  should  so  stand  that  the  knife  strikes  it  first  on  one  corner.  The 
knife  should  be  moved  slowly  in  the  slideway  and  pressure  upon  it 
should  be  carefully  avoided. 

Sectioning  with  the  Knife  Placed  Transversely. — Screw  the  knife 
down  perpendicular  to  the  long  axis  of  the  microtome,  turn  the  paraffin 
block  so  that  the  blade  will  strike  it  first  on  a  flat  surface.  The  knife 
should  be  rapidly  moved  with  a  planing  movement  and  then  the  sections 
will  adhere  to  one  another  at  their  edges  and  form  long  ribbons.  When 
the  paraffin  is  of  the  right  consistence  the  first  section  lies  smoothly  on 
the  blade  and  is  shoved  by  the  second  section  in  the  direction  of  the 
back  of  the  blade.  If  however  the  first  sections  show  an  inclination  to 
curl  and  fall  over  the  edge,  they  must  then  be  carefully  held  with  a  deli- 
cate sable  brush  and  led  back  to  the  right  position.  Ribbon-cutting  is 
most  successful  when  the  sections  have  a  thickness  of  o.oi  of  a  milli- 
meter;  thicker  sections  easily  curl  and  do  not  readily  adhere  to  one 
another  at  their  edges. 

OBSTACLES  IN  SECTIONING  AND  THEIR  REMEDY. 

Every  one  who  has  worked  with  paraffin  is  probably  able  to  explain 
many  an  unsuccessful  attempt. 

I.  The  knife  glides  over  the  object  and  cuts  a  partial  section  or 
none.  The  reason  for  this  may  lie  in  the  microtome  ;  the  slideway  may 
not  be  clean  ;  examine  the.  vertical  portion  of  the  slideway.  Or  the 
knife  is  not  sharp  enough,  or  the  under  surface  has  paraffin  attached  to 


408  HISTOLOGY. 

it ;  in  the  latter  case  remove  the  knife  and  with  a  cloth  wetted  with  tur- 
pentine carefully  cleanse  it.  Knives  with  thin  backs  buckle  if  the  distal 
end  of  the  blade  is  used  ;  thus  it  happens  that  when  the  knife  is  obliquely 
placed  the  blade  cuts  the  tissue  only  at  the  edge  where  it  first  touches 
and  glides  over  the  rest  without  cutting  it.  In  microtomes  of  earlier 
construction  the  cause  of  this  often  lies  in  the  unsatisfactory  manner  in 
which  the  block  of  paraffin  is  secured. 

Secondly,  the  trouble  may  be  found  in  the  object  ;  it  may  be  too 
hard,  or  of  very  unequal  resistance,  or  poorly  embedded  ;  in  the  latter 
case  there  are  two  possibilities.  Either  the  preparation  was  not  thor- 
oughly dehydrated,  in  which  case  it  exhibits  opaque  spots  or  it  still  con- 
tains chloroform  ;  in  this  case  it  is  soft,  and  light  pressure  with  a  needle 
on  the  surface  leaves  a  mark  or  even  presses  out  fluid.  In  both  cases 
the  procedure  of  embedding  must  be  repeated,  reversing  the  series  of 
processes  to  the  absolute  alcohol  (in  the  latter  case  to  the  paraffin  bath). 

Finally,  the  consistence  of  the  paraffin  may  be  at  fault. 

2.  The   sections  curl.     This  can   be   prevented  by  holding  a  small 
sable  brush  or  bent  needle  lightly  against  the  sections  as  they  are  cut.* 
The  cause  of  this  curling  lies  in  the  hardness   of  the  paraffin,  which  is 
also  responsible  for — 

3.  The  sections  break.     The  usefulness  of  the  paraffin  depends  in  a 
high  degree  on  the  outer  temperature.     If  the  paraffin  is  too.  hard  do 
not  endeavor  to  reduce  its  consistence  by  the  admixture  of  soft  paraffin, 
— this  is  the  last  resource, — but  employ   simpler  measures.      Cut  the 
sections  near  a  stove  or  near  a  lamp  ;  often  slight  warming  of  the  knife 
is   sufficient.     Even  very  good  paraffin  crumbles  when  cut  with  a  cold 
knife. 

4.  The  sections  fold  and  become  pressed  together.     As  a  result  of 
this  the  sectioned  objects  acquire  a  false  form.     The  reason  for  this  lies 
in  a  too  soft  paraffin.     This  difficulty  may  be  overcome  by  frequently 
placing  the  block  in  cold  water  or  by  cutting  the  sections  in  a  cold  room 
(in  summer,  in  the  morning  hours). 

CELLOIDIN  OBJECTS. 

The  embedded  object  is  to  be  trimmed  so  that  it  is  surrounded  by 
a  stratum  of  celloidin  only  one  or  two  millimeters  thick  ;  clamp  the  knife 
obliquely,  so  that  it  makes  a  very  acute  angle  with  the  long  axis  of  the 
microtome.  The  knife  must  be  moistened  with  70  per  cent,  alcohol  by 
means  of  a  sable  brush  ;  this  must  be  done  after  every  second  or  third 
section  is  cut.  The  sections  should  be  removed  with  a  sable  brush  and 
transferred  to  a  dish  containing  70  per  cent,  alcohol.  Very  thin  sections 
(less  than  0.02  mm.)  cannot  be  cut  unless  the  celloidin  has  been  hard- 
ened. 

*  A  "section -smoother  "  for  microtomes  in  which  the  object  is  elevated  vertically  is  made 
by  Kleinert  of  Breslau.  See  further,  Born,  "  Zeitschr.  f.  wissensch.  Mikroskopie,"  Bd.  x,  p. 
157- 


MICROTOME    TECHNIC.  409 


PRESERVATION  OF  SECTIONS. 

PARAFFIN  OBJECTS. 

If  the  sections  are  not  veiy  thin  and  are  not  in  ribbons,  they  may 
be  placed  in  a  capsule  with  5  c.c.  of  turpentine  and  when  the  paraffin  is 
dissolved  transferred  to  a  second  capsule  with  turpentine.  From  this 
the  sections,  if  the  tissue  has  been  stained  in  bulk,  are  carried  to  a  slide 
and  mounted  according  to  the  directions  given  on  page  44.  If  the  sec- 
tions are  unstained,  transfer  them  from  turpentine  to  5  c.c.  of  ninety-five 
per  cent,  alcohol,  which  is  to  be  changed  in  five  minutes..  In  another 
two  minutes  the  sections  may  be  stained.  In  the  case  of  serial  sections 
and  very  thin  sections,  it  is  necessary  to  fasten  the  dry  sections  on  the 
slide.  The  slide  must  be  absolutely  clean  ;  wash  it  with  alcohol  and  dry 
it  with  a  clean,  not  oily,  cloth  or  place  it  for  a  half  hour  in  cold  soap- 
suds. On  the  well-dried  slide  arrange  the  sections  (or  portion  of  the 
"  ribbon  "),  and  at  the  edge  of  the  same  place  a  drop  of  distilled  water 
by  means  of  a  delicate  sable  brush.  Another  section  (or  portion  of  the 
ribbon)  is  now  placed  on  the  slide,  another  drop  of  water  added,  and  so  on 
until  the  slide  is  covered.  It  does  not  matter  if  the  sections  float.  Pass 
the  slide  through  a  spirit-flame  or  place  it  for  from  one  to  three  minutes 
in  the  oven  ;*  on  being  slightly  warmed,  the  sections  spread  out  flat  and 
smooth.  Then  arrange  them  with  a  needle  and  by  slightly  inclining 
the  slide  let  the  water  flow  off,  or  absorb  it  with  a  strip  of  filter-paper 
and,  protected  from  dust,  let  the  whole  dry.  On  the  following  day  pour 
turpentine  over  the  slide  and  if  the  sections  are  already  stained  mount 
them  in  damar.  In  case  the  sections  are  not  stained  the  turpentine  is  to 
be  wiped  off  and  the  slide  placed  in  ninety-five  per  cent,  alcohol. f  After 
five  minutes  take  the  slide  from  the  alcohol,  which  is  to  be  quickly  wiped 
ofT around  the  sections,  breathed  upon,  and  either  placed  in  the  stain  or 
covered  with  a  drop  of  the  solution.  Then  slowly  transfer  the  slide  to 
a  dish  with  distilled  water  and  preserve  it  in  dilute  glycerol  (p.  45),  or 
with  the  customary  preliminary  treatment  with  ninety-five  per  cent, 
alcohol  and  oil  of  bergamot  (p.  45),  mount  it  in  damar. 

CELLOIDIN  OBJECTS. 

Place  the  sections  in  a  dish  containing  20  c.c.  of  ninety  per  cent, 
alcohol.  If  the  tissue  has  not  been  previously  stained  in  bulk,  staining 
in  bulk  to  be  preferred,  the  sections  may  be  subsequently  stained  ;  but 

*  The  paraffin  must  not  be  allowed  to  melt ;  the  resulting  mixture  of  melted  paraffin  and 
water  is  not  soluble  in  turpentine. 

f  The  turpentine,  also  the  alcohol,  must  be  quickly  wiped  off,  because  the  sections  are 
rendered  useless  if  they  are  allowed  to  become  dry.  Care  must  also  be  exercised  in  placing  the 
staining  fluid  on  the  sections,  which  it  should  completely  cover.  Loosening  of  the  sections 
occurs  when  there  is  not  enough  water  between  the  section  and  the  slide — the  water  must  be 
evenly  diffused  between  the  two.  The  section  may  also  be  fastened  to  the  cover-glass,  but  this 
method  necessitates  the  use  of  larger  quantities  of  the  staining  solution,  alcohol,  and  other 
reagents. 


4IO  HISTOLOGY. 

anilin  colors  cannot  be  used,  since  they  also  stain  the  celloidin  ;  even  hema- 
toxylin  imparts  a  light-blue  tint  to  the  celloidin.  The  sections  must  not 
be  placed  in  stronger  alcohol,  since  this  dissolves  the  celloidin  ;  they  are 
to  be  taken  from  the  ninety  per  cent,  alcohol  and  placed  in  chemically 
pure  amyl  alcohol  and  then  transferred  to  xylol ;  when  the  clearing  is 
completed  mount  them  in  xylol-balsam. 

Serial  sections  of  celloidin  objects  are  used  only  for  special  purposes, 
for  example,  for  the  central  nervous  system.  See  the  articles  by  Wie- 
gert  in  the  "  Zeitschrift  fur  wissenschaftliche  Mikroskopie,"  Bd.  ii., 
p.  490,  Bd.  iii.,  p.  480,  Bd.  iv.,  p.  209.  The  negative  varnish  recom- 
mended in  the  article  is  to  be  obtained  of  Dr.  Grubler. 


BOOKS   OF    REFERENCE. 


GENERAL  WORKS. 

Kolliker,  A. — Handbuch  der  Gewebelehre  des  Menschen.     6.  Auflage.   Leipzig  (Engelmann), 

1896. 
Schafer,  E.  A. — Histology  and  Microscopical  Anatomy, — in   Quain's  Elements  of  Anatomy, 

Tenth  Edition,  London  and  New  York  (Longmans,  Green  &  Co.),  1896. 


SPECIAL  WORKS. 

THE  CELL. 

Bergh,  R.  S. — Vorlesungen  iiber  die  Zelle  und  die  einfachen  Gewebe.     Wiesbaden,  1894. 
Henneguy,  L.  F. — Lecons  sur  la  cellule.     Paris  (Carre),  1896. 

Hertwig,  O. — Die  Zelle  und  die  Gewebe.  I.  Buch :  Allgemeine  Anatomic  und  Physi- 
ologic der  Zelle.  Jena  (Fischer),  1892.  Translation,  published  by  Macmillan,  London 
and  New  York,  1895. 

Wilson,  E.  B. — The  Cell  in  Development  and  Inheritance.  New  York  and  London  (Mac- 
millan), 1896. 

THE  TISSUES. 

Bergh,  R.  S. — Vorlesungen  iiber  die  Zelle  und  die  einfachen  Gewebe.     Wiesbaden,  1894. 
Hertwig,  O. — Die  Zelle  und  die  Gewebe.     II.  Buch:   Allgemeine  Anatomic  und  Physiologic 
der  Gewebe.     Jena  (Fischer),  1898. 

THE  BLOOD. 

Cabot,  R.  C. — A  Guide  to  the  Clinical  Examination  of  the  Blood  for  Diagnostic  Purposes. 
New  York  (Wood  &  Co.),  1897. 

THE  NERVOUS  SYSTEM. 

Dejerine,  J. — Anatomic  des  centres  nerveux.     Tome  I.     Paris  (Rueff  et  Cie),  1895. 

Edinger,  L. — Vorlesungen  iiber  den  Bau  der  nervosen  Centralorgane.  5.  Auflage.  Leip- 
zig, 1897. 

Gehuchten,  A.  van. — Anatomic  du  systeme  nerveux  de  1'homme.  2  Edition.  Louvain, 
1897. 

Golgi,  C. — Untersuchungen  iiber  den  feineren  Bau  des  centralen  und  peripheren  Nervensys- 
tems.  Jena,  1894. 

Lenhossek,  M.  von. — Der  feinere  Bau  des  Nervensystems  im  Lichte  neuester  Forschungen. 
2.  Auflage.  Berlin  (Fischer),  1895. 

Ramon  y  Cajal,  S. — Xeue  Darstellung  vom  histologischen  Bau  des  Centralnervensystems. 
(Arch.  Anat.  und  Physiol.,  Anat.  Abth.,  1893). 

Les  nouvelles  idees  sur  la  structure  du  systeme  nerveux  chez  rhomme  et  chez  les 
vertebres.     Paris  (Reinwald  &  Co.),  1894. 

411 


412  BOOKS    OF    REFERENCE. 

THE  INTESTINES. 

Oppel,  A. — Lehrbuch  der  vergleichenden  mikroskopischen  Anatomic  der  Wirbelthiere.    I.  Der 
Magen,  II.  Schlund  und  Darm.     Jena  (Fischer),  1896-1897. 

THE  SENSORY  ORGANS. 
Pollitzer,  A. — Die   anatomische   und   histologische    Zergliederung  des  menschlichen  .Gehor- 

organs  im  normalen  und  kranken  Zustande.      Stuttgart  (Enke),  1889. 
Ramon  y  Cajal,  S. — La  retine  des  vertebres.      (La  Cellule,  ix,  1893.) 
Schwalbe,  G. — Lehrbuch  der  Anatomic  der  Sinnesorgane.      Erlangen,  1887. 

TECHNIC. 
Apathy,  S. — Die  Mikrotechntk  der  thierischen  Morphologic.      I.  Abtheilung.      Braunschweig 

(Bruhn),  1896. 
Behrens,  W.,  Kossel,  A.,  and  Schieffcrdecker,  P. — Das  Mikroskop  und  die  Methoden  dtr 

mikroskopischen  Untersuchung.      Braunschweig  (Bruhn),  1889. 
Bohm,  A.,  and  Oppel,  A. — Taschenbuch  der  mikroskopischen  Technik.     3.  Auflage.     Miin- 

chen  (Oldenbourg),  1896. 
Lee,  A.  B. — The  Microtomist's  Vade-mecum.     A  Handbook  of  the  Methods  of  Microscopic 

Anatomy.     Third  Edition.     Philadelphia  (Blakiston),  1896. 


NDEX. 


A. 

Acervulus  cerebri,  182,  201 
Acetic  acid,  20 
Achromatin,  57 
Acid  alcohol,  25 
"     mixture,  24 
Adenoid  tissue,  125 
diffuse,  125 
of  the  intestines,  234 
of  the  lymph-glands,  123 
of  the  pharynx,  223 
of  the  tongue,  220 
Adipose  tissue,'8o,  86,  88 
Agminated  nodules,  235 
Alcohol,  19,  20 
acid,  25 
one-third,  20 

Alcohol-ether  mixture,  132,  405 
Alcohol-glycerol  mixture,  406 
Alum-carmine,  24 
Alveolar  ducts,  267 
Ameboid  movement,  59 
Ammonium  picrate,  25 
Amphypyrenin,  57 
Anaphase,  62 
Anisotropic  substance,  92 
Appendix  epididymidis,  295 

testis,   295 
Arachnoid,  183 

granulations  of,  184 
Arcuate  fibers,  342 
Arcus  tarseus,  368 

"        externus,  368 
Areolar  tissue,  80 
Arrectores  pilorum,  326 
Arteries,  in 

classification  of,  in 
Astrocyle,  171 
Astrosphere,  60 
Attraction-sphere,  60 
Auditory  sand,  378 
Auerbach's  plexus,  238 
Axis-cylinder,  98 
Axon,  98 
Axoneurons,  164 

B. 

Baillarger's  stripes,  175 
Basement  membrane,  Si 
Bergamot  oil,  22 


Berlin  blue,  44 
Bile,  251 

Bile-capillaries,  247 
Bioplasts,  57 
Blood,  118 

cells  of,  118 

elementary  granules,  120 

examination  of,  for  legal  purposes,  133' 

fibrin,  120 

hematoblasts,  121 

permanent  preparation  of,  132 

plasma,  118 

-platelets,  120 
Blood-cells,  118 

colored,   118 

colorless,  119 
Blood-crystals,'  12 1 
Blood-platelets,  120 
Blood-vessels,  109 

arteries,  in 

blood-vessels  of,  117 

capillaries,  Il6 

epithelium  (endothelium)  of,  131 
external  elastic  membrane,  112 
internal  elastic  membrane,  in 
lymph-spaces  of,  117 
nerves  of,  117 
tunica  externa,  114 
tunica  intima,  113 
tunica  media,  112 
valves,  116 
veins,  114 
Bone,  137 

articulations  of,  142 
blood-vessel's  of,  142 
canaliculi,  139 
cells,  85 

circumferential  lamelke,  138 
development  of,  145 
endochondral,  146 
growth  of,  151 
haversian  canals,  138 
haversian  lamellne,  138 
haversian  systems,  138 
Howship's  lacuna?,  152 
intermembranous,  146 
interstitial  lamellae,  138 
lacunae,  85,  139 
lymph-vessels  of,  142 
marrow  of,  139 
matrix  of,  84,  85 


413 


INDEX. 


Bone,  nerves  of,  142 
osteoblasts,  149 
osteoclasts,  152 
periosteum,  137 
primary,   146 
resorption  of,  152 
secondary,  146 
Sharpey's  fibers,  142 
Volkmann's  canals,  139 

Bowman's  capsule,  277 
"          glands,  395 

membrane,  341 

Brain,  172 

cells  of,  201 
cerebellar  cortex,  176 
cerebral  cortex,  172 
corpora  quadrigemina,  172 
corpora  striata,  172 
ganglia  of,  176 
Golgi  staining  of,  201 
gray  substance  of,  172 
hypophysis  cerebri,  182 
optic  thalami,  172 
pineal  body,  182 
ventricles  of,  176 
white  substance  of,  181 

Brain-sand,  182,  201 

Bronchi,  267,  274 

blood-vessels  of,  271 
cartilages  of,  268 
excretory  division,  267 
glands  of,  269 
mucosa  of,  269 
muscle-fibers  of,  268 
respiratory  division,  267 

Brunner's  glands,  234 

Brushborder,  66,  280 

Budding,  62 

Bursae,  157 

C. 

Cajal's  cell,  172 
Calcification,  center  of,  147 
Canada  balsam,  23 
Canalized  fibrin,  315 
Capillary  blood-vessels,  Il6 

development  of,  Il6,  131 
Cardiac  muscle,  109 
Carmine,  alum-,  24 

borax-,  24. 

neutral  solution  of,  24 
Carotid  gland,  Il8 
Cartilage,  82,  89 

articular,  145 

bronchial,  268 

capsule,  82 

cells,  82 

costal,  145 

elastic,  84,  90 

epiphyseal,  151 

fibro  ,  84,  90 

hyaline.  83    — 

lacunae  of,  82 

matrix  of,  82 

perichondrium,  145     • 

varieties  of,  83    _- 


Caruncula  lacrymalis,  368 
Cells,  56 

basket.  180 

bone,  85 

Cajal's,  172 

cartilage,  82 

chief,  225 

Claudius's,  384 

column,  165 

commissure,  165 

concentric,  350 

cone-visual,  352 

decidual,  310 

Deiters's,  166,  383 

endothelial,  66 

eosinophilous,  140 

ependymal,  170 

epithelial,  65 

fat,  79 

fat,  serous,  80 

fiber,  378 

fixed,  80 

forms  of,  58 

ganglion,  99 

giant,  140,  152 

glandular,  69 

glia,  170 

goblet,  71,  232,  269,  306 

granule,  79 

growth  of,  63 

gustatory,  399 

hair,  378 

Hensen's,  384 

internal,  164,  166 

interstitial,  289 

Langerhans's,  190 

length  of  life  of,  63 

liver,  244 

marrow,  140 

mast,  79 

mossy,  176 

motion  of,  59 

motor  nerve-,  164 

multiplication  of,  60 

olfactory,  394 

parietal,  225 

pigment,  65,  79 

pillar,  382 

plasma,  79 

plurifunicular,  166 

prickle,  68 

Purkinje's,  179 

reproduction  of,  60 

rod-visual,  352 

secretory  activity  of,  63 

secretory  products  of,  63 

size  of,  59 

spider,  171 

structure  of,  56 

sustentacular,  349,  383,  394,  399 

tactile,  191 

tegmental,  399 

tendon,  158 

undifferentiated,  55 

vasoformative,  131 

vital  properties  of,  59 


INDEX. 


415 


Cells,  wandtJrnig,  80 
Cell-division,  bo 
direct,  60 
duration  of,  62 
indirect,  60 
Cell-membrane,  58 
Cell- patch,  315 
Cement-substance.t.  64 
Central-spindle,  fri 
Centrosome,  58 
Cerebellar  cortex,  176 

basket  cells  of,  180 
cells  of  Purkinje,  179 
Golgi  staining  of,  201 
granule  layer  of,  177 
molecular  layer  of,  179 
neuroglia  of,  1 80 
white  substance  of,  181 
Cerebral  cortex,  172 
cells  of  Cajal,  172 
interradial  reticulum,  175 
molecular  zone,  172 
radiating  bundles  of,  174 
stripes  of  Gennari,  173 
superradial  reticulum,  175 
tangential  fibers,  172 
zone  of  large  pyramidal  cells,  174 
zone  of  polymorphous  cells,  174 
zone  of  small  pyramidal  cells,  174 
Cerumen,  389 
Ceruminous  glands,  389 
Chondrin,  83 
Choriocapillaris,  345 
Choroid,  344 

boundary  zone  of,  345 
lamina  basalis,  345 

"      choriocapillaris,  345 
"      vasculosa,  344 
stroma  of,  344 
tapetum  cellulosum,  344 

"       fibrosum,  345 
Chromatin,  57 
Chromic-acetic  acid,  22 
Chromic-acetic-osmic  acid.  22 
Chromic  acid,  20,  30 
Chromosomes,  60 
Ciliary  body,  345 
"      muscle,  346 
"      processes,  345 
Ciliated  epithelial  cells,  66 
Clearing,  46 
Close-skein,  61 
Coccygeal  gland,  118 
Cochlea,  378 
Cohnheim's  fields,  93 
Coil-glands,  332 

distribution  of,  333 
secretion  of,  333 
Collateral  fibers,  101 
Colored  blood-corpuscles,  118 
development  of,  121 
hemoglobin,  119 
stroma  of,  Il8 

Colorless  blood-corpuscles,  119 
granules  of,  119 
varieties  of,  119 


Colostrum,  337 
Column-cells,  165 
Cone-fibers,  353 
Cone-granules,  353 
Congo  red,  25 
Conjunctiva,  palpebral,  365 

"  scleral,  367 

Conjunctival  recesses,  367 
Connective  tissue,  76 

arrangement  of,  80 
blood-vessels  of,  86 
cells  of,  78 
elastic,  78 
fibrillar,  77 

intercellular  substance  of,  76 
interstitial,  80 
lymph-spaces  of,  86 
mucous,  77 
nerves  of,  86 
reticular,  8l 
wandering  cells  of,  80 
Con  us  medullaris,  164 
Corium,  321 
Cornea,  341,  372,  373 

anterior  elastic  lamina  of,  341 
arcuate  fibers  of,  342 
blood-vessels  of,  373 
canaliculi  of,  342 
corpuscles  of,  343 
endothelium  of,  344 
epithelium  of,  341 
nerves  of,  364,  373 
postei  ior  elastic  lamina  of,  343 
spaces  of,  343 
substance  proper,  342 
Corona  radiata,  301 
Corpora  quadrigemina,  172 

"        striata.  172 
Corpuscula  amylacea,  183 
Corpus  Highmori,  289 

"       luteum,  301 
Corpuscles,  articular,  194 
concentric,  274 
corneal,  343 
Grandry's,  192 
genital,  194 
Hassall's,  274 

Herbst  and  Key-Retzius's,  194 
lamellar,  193 
Malpighian,  126,  277 
Merkel's,  192 
Pacinian,  193 
salivary,  221 
tactile,  194 
Vater's,  193 

Wagner  and  Meissner's,  194 
Cover-glass  cement,  23,  45 
Cover-glasses,  18 
Cox-Golgi  method,  41 
"       "      mixture,  21 
Crescents  of  Giannuzzi,  74 
Crypts  of  Lieberkuhn,  230 
Cumulus  ovigerus,  301 
Cupula,  37g 
Cytoblastema,  60 
Cytogenous  tissue,  81 


416 


INDEX. 


D. 


Dahlia,  alum-carmine,  25 
Damar  varnish,  23 
Daughter-stars,  62 
Decalcifying,  33 
Decidua  graviditatis,  308 

'        menstrualis,  307 

'        placentalis  subchorialis,  316 

'        reflexa,  309 

'        serotina,  309 

'        vera,  309 
Decidual  cells,  310 
Demilunes,  74,  240 
Dendrites,  97 
Dentine,  86,  210 
Descemet's  membrane,  343 
Deutoplasm.  300 
Diarthroses,  143 
Diaster,  62 

Direct  cell-division,  60 
Discus  proligerus,  301 
Dissection,  27 
Drawing,  52 
Duodenal  glands,  234 
Dura,  183 


E. 
Ear,  376-390 

arcus  spiralis,  382 

arteries  of,  385 

auditory  hairs,  378 

auditory  teeth,  380 

bony  labyrinth,  377 

cells  of  Claudius    384 

cells  of  Deiters,  383 

cells  of  Hensen,  384 

ceruminous  glands,  389 

cochlea,  377,  378 

cristse  acusticse,  377 

cupula,  378 

ductus  cochlearis,  378 

ductus  endolymphaticus,  388 

ductus  perilymphaticus,  388 

endolymph,  377,387 

epithelium  of  cochlea,  381 

external,  388 

fiber-cells,  378 

foramina  nervina,  381 

ganglion  spirale,  385 

hair-cells,  378 

internal,  377 

labium  tympanicum,  379 

labium  vestibulare,  379 

lamina  spiralis  membranacea,  381 

ligamentum  spirale,  379 

limbus,  379 

lymph-channels  of,  387 

maculae  cribrosae,  377 

membrana  basilaris,  381 

membranous  labyrinth,  377 

middle,  388 

mucosa  of  eustachian  tube,  388 

mucosa  of  tympanic  cavity,  388 

nerves  of,  384,  385 

Nuel's  space,  384 


Ear,  otoliths,  378 

perilymph,  377 

pillar-cells,  382 

prominentia  spiralis,  380 

Reissner's  membrane,  380 

sacullus,  377 

semicircular  canals,  ^Ak 

spiral  organ,  38^ 

stria.-  vascularisMto 

sulcus  spiral^  j^ 

tunnel,  382 

ic  lamella,  381 
377 
eins  of,  386 

vestibular  membrane,  379 

zona  pectinati,  382 

zona  perforata,  381 

zona  tecta,  382 
Egi^-protoplasm,  300 
flhrlich's  dry  method,  132 
Elastic  tissue,  78 
Elementary  granules,  120 

"  organism,  56 

Embedding,  404 

in  celloidin,  405 

in  paraffin,  404 

in  liver,  35 
Enamel  prisms,  21 1 
Encircling  fibers,  79 
Endaxoneurons.  164 
End-bulbs,  192 
Endogenous  cell -formation,  62 
Endothelium,  66 
Eosin,  25 

Ependyma  of  the  ventricles,  176 
Epidermis,  323 
Epididymis,  293 
Epiglottis,  266 
Epiphysis.  182 
Epithelium,  65 

brushborder  of,  66 

ciliated,  66 

columnar,  65 

cubical,  6^ 

cuticular  zone  of,  66 

cylindrical,  65 

distribution  of,  66 

germinal,  of  ovary,  299 

glandular,  69,  71 

goblet  cells  of,  7 1 

isolation  of,  28 

neuro-,  66 

of  lens,  359 

of  mucous  membranes,  208 

pavement,  65 

pigmenteri.  65 

prickle-cells  of,  68 

respiratory,  269 

secretory  activity  of,  69 

squamous,  65 

terminal  bars  of,  68 

top-plate  of,  65 

transitional,  65,  284 

varieties  of,  66,  67 
Eponychium,  326 
Epoophoron,   303 


INDEX. 


417 


ErythroMSsts,  121, 
EsonMjus,  223 
F^Rchian  tube,  388 
flfoplasm,  56 
Eye,  34l-369 

blood-vessel 

canal  of  Pe 

canal  of  Sc! 

choriocapillaris,  345 

choroid,  344 

ciliary  body,  345 

ciliary  muscle,  346 

ciliary  processes.  344 

color  of  iris,  347 

conjunctiva,  344 

cornea,  341 

fovea  centralis,  353 

ganglion  retinae,  351 

hyaloid  canal,  363 

hyaloid  membrane,  360 

irido-corneal  angle,  347 

iris,  346 

lacrymal  canaliculi,  369 

lacrymal  caruncle,  368 

lacrymal  glands,  368 

lacrymal  sac,  369 

lamina  cribrosa,  358 

lamina  fusca  sclerae,  344 

lamina  suprachoroidea,  344 

lens,  358 

ligamentum  pectinatum  iridis,  347 

macula,  353 

naso-lacrymal  duct,  369 

nerves  of,  364 

optic  nerve,  357 

ora  serrata,  349,  355 

perichoroidal  space,  364 

pigment  layer  of  iris,  347 

plica  semilunaris,  367 

retina,  348 

sclera,  344 

sheaths  of  optic  nerve,  357 

spaces  of  Fontana,  341 

spatia  zonularia,  360 

suspensory  ligament,  360 

tapetum  cellulosum,  344 

tapetum  fibrosum,  344 

Tenon's  space,  364 

tunica  externa,  341 

tunica  interna,  348 

tunica  media,  344 

venae  vorticosae,  363 

vitreous  body,  360 

zone  of  Zinn,  360 

zonula  ciliaris,  360 
Eyeball,  blood-vessels  of,  360 

coats  of,  341 

contents  of,  341 

lymph-channels  of,  363 

nerves  of,  364 
Eyelashes,  365 
Eyelids,  365-375 

blood-vessels  of,  368 

caruncula  lacrymalis,  368 

cilia,  365 

fornix  conjunctivae,  367 
27 


Eyelids,  glands  of,  367 
integument  of,  365 
lymph-vessels  of,  368 
muscles  of,  366 
nerves  of,  368 
ocular  conjunctiva,  367 
palpebral  border,  365 
palpebral  conjunctiva,  365 
plica  semilunaris,  367 
tarsus,  366 

F. 

Fallopian  tube,  303 
Fasciae,  157,  159 
Fascia  palpebralis,  366 
Fenestrated  membranes,  78 
Fibers,  arcuate,  342 

cone-,  353 

encircling,  79 

intergeminal,  401 

intrageminal,  401 

lattice-,  251 

lens-,  358 

mossy-,  181 

rod-,  352 

stem-,  168 
Fiber-body,  352 
Fiber- cell,  378 
Fiber-crate,  350 
Fixation  of  tissues,  30 
Flemming's  mixture,  22,  32 
Formic  acid,  22 
Fovea  centralis,  355 
Fresh  objects,  examination  of,  48 
Fundus  foveae,  355 

glands,  225 

G. 

Gall-bladder,  244 
Ganglia,  187 

cerebral,  176 

spinal,  187 

sympathetic,  189 
Ganglion-cells,  99 

apolar,  99 

bipolar,  99 

multipolar,  99 

unipolar,  99 
Ganglioneurons,  164 
Ganglion  retinas,  351 

"        spirale,  385 
Gastric  glands,  225 

"       pits,  225 
Gemmation,  63 
Generatio  aequivoca,  60 
Genitalia,  317 
Gennari  stripes,  175 
Germinal  center,  123 
Germ-layers,  55 
Glacial  acetic  acid,  20 
Glands,  71 

accessory  mammary,  336 

accessory  tear-,  367 

alveolar,  71 


INDEX. 


Glands,  areolar,  336 

Bartholin's,  317 

Bowman's,  395 

Brunner's,  234 

ceruminous,  389 

ciliary,  365 

classification  of,  71 

coil,  332 

Cowper's,  296 

dehiscent,  73 

duodenal,  234 

fundus,  225 

gastric,  225 

Harder's,  376 

intestinal,  230 

lacrymal,  368 

Lieberkuhn's,  230 

Litri's,  286 

mammary,  335 

Meibomian,  367 

mixed  salivary,  240 

Moll's,  365 

Montgomery's,  336 

mucous  salivary,  240 

Nuhn's,  222 

olfactory,  395 

parotid,  240 

peri-urethral,  286 

salivary,  239 

sebaceous,  331 

serous  salivary,  240 

structure  of,  71, 

sublingual,  240 

submaxillary,  240 

sudoriparous,  332 

sweat-,  332 

tarsal,  367 

tear,  368 

trachoma,  367 

tubular,  71 

Tyson's,  332 
Glomus  caroticum,  118 

"      coccygeum,  118 
Glycerol,  22 
Goblet-cells,  71 
Gold  chlorid,  22 
Golgi's  method,  41 
"       mixture,  21 
Graafian  follicle,  300 

cumulus  ovigerus,  301 

discus  proligerus,  301 

liquor  folliculi,  300 

stratum  granulosum,  301 

theca  folliculi,  301 
Granula,  57 
Ground-substance,  64 


H. 

Hair,  326 

-bulb,  326 

color  of,  327 

cortical  substance  of,  327 

cuticle  of,  327 

development  of,  329 


Hair,  distribution  of,  326 

elements  of,  326 

follicle  of,  328 

growth  of,  330 

medulla  of,  327 

-papilla,  326 

renewal  of,  330 

roots  of,  326 

shaft  of,  326 

shedding  of,  330 
Hair-follicle,  326 

elements  of,  328 
Hardening  of  tissues,  33 
Heart,  109 

annuli  fibrosi,  no 

blood-vessels  of,  no 

endocardium,  109 

epicardium,  no 

lymphatics  of,  iio 

muscle-fibers  of,  109 

myocardium,  109 

nerves  of,  in 

valves  of,  no 
Hematoblasts,  121,  141 
Hematoxylin — 

^  Delafield's,  23,  39 
*  Hansen's,  23,  36 

Weigert's,  24 
Hemoglobin,  119 
Howship's  lacunae,  152 
Hyaloid  canal,  363 

"        membrane,  8l 
Hyaloplasm,  57 
Hydatid  of  Morgagni,  295 
Hydrochinone  developer,  21 
Hydrochloric  acid,  20 
Hypophysis  cerebri,  182 


I. 


Illumination,  central,  50 
"  lateral,  50 

"  oblique,  50 

Indirect  cell-division,  60 

Injecting,  43,  44 

Instruments,  1 8 
care  of,  27 

Intercellular  bridges,  68 
"          substance,  63 

Intermediate  lacunae,  129 

Internodal  segments,  105 

Internode,  105 

Interstitial  cells,  289 
"          granules,  93 
'  <          tissue,  80 

Intervillous  spaces,  314 

Intestine,  229 

blood-vessels  of,  236 
crypts  of  large,  230 
cuticular  border  of,  232 
duodenal  glands,  234 
epithelium  of  small,  231 
goblet-cells  of,  232 
intestinal  glands,  230 
Lieberkuhn's  glands,  230 


V 


INDEX. 


419 


Intestine,  lymph-nodules  of,  234 

lymph-vessels  of,  238 

mucosa  of,  229 

muscular  tissue  of,  236 

nerves  of,  238 

Peyer's  patches,  235 

plica  circularis,  230 

regeneration  of  epithelium,  232 

solitary  follicles  of,  234 

triple  staining  of,  260 

valvulae  conniventes,  229 

villi,  230 

Intra-epithelial  nerve-fibers,  190 
Involuntary  muscle,  90,  94 
Iridal  processes,  347 
Irido-corneal  angle,  347 
Iris,  346 
Isolating,  28 
Isotropic  substance,  92 


K. 

Karyokinesis,  60,  64 
Karyosomes,  57 
Keratohyalin  granules,  323 
Kidney,  277-286 

blood-vessels  of,  280 

brushborder,  280 

capsule  of  the  glomerulus,  277 

connective  tissue  of,  280 

cortex  of,  277 

epithelium  of,  279,  280 

Henle's  loop,  277 

lymph-vessels  of,  283 

medulla  of,  277 

medullary  rays,  277 

nerves  of,  283 

papillae  of,  277 

papillary  duct,  277 

renal  corpuscle,  277 

uriniferous  tubules,  277 
Kleinenberg's  solution,  21,  31 


L. 

Lacrymal  glands,  368-376 
"         canaliculi,  369 
"         duct,  naso-,  369 
"         sac,  369 

Lamellar  corpuscles,  193 

Lamina  basalis,  345 

'       choriocapillaris,  345 
'       cribrosa,  358 
'       fusca  sclerae,  344 
'       suprachoroidea,  344 
'       vasculosa,  344 

Lanugo,  328 

Larynx,  266 

blood-vessels  of,  266 
cartilages  of,  266 
lymph-vessels  of,  266 
nerves  of,  267 
solitary  nodules  of,  266 
vocal  cords,  266 


Lens,  341,  358 

epithelium  of,  359 
Lens-capsule,  359 
Lens-fibers,  358 
Lens-stars,  359 
Leucocytes,  119 

classification  of,  119 

formation  of,  124 

granules  of,  1 20 

Ligamentum  iridis  pectinatum,  347 
Ligamentum  spirale,  379 
Linin,  57 

Lithium  carbonate,  solution  of,  24 
Litri's  glands,  286 
Liver,  243-264 

bile-capillaries,  247 

blood-vessels  of,  247 

capsule  of,  251 

capsule  of  Glisson,  251 

cells  of,  244 

cords  of  cells,  246 

hepatic  duct,  243 

interlobular  bile-ducts,  244 

interlobular  connective  tissue,  244 

lobules  of,  243,  252 

lymphatics  of,  251 

nerves  of,  251 

relation  of  bile-capillaries  to  cells  of,  247, 
248 

secretion  of,  251 

tubular  structure  of,  25 1 

vasa  aberrantia,  244 
Loose  skein,  61 
Lungs,  267-274 

alveolar  ducts,  267 

alveoli,  267 

blood-vessels  of,  271 

elastic  fibers  of,  270 

infundibula  of,  267 

interlobular  tissue  of,  270 

lobules  of,  268 

lymph-vessels  of,  272 

nerves  of,  272 

pigmentation  of,  270 

respiratory  bronchioles,  267 

respiratory  epithelium,  269 

terminal  bronchioles,  267 

terminal  vesicles,  267 
Luaula  of  nail,  326 
Lymph,  126 

"        canaliculi,  122 
"        corpuscles,  126 
"        spaces,  86 
Lymphatic  tissue,  125 

diffuse,  125 

Lymph-channels  of  the  central   nervous  sys- 
tem, 185 

Lymph-glands,  122 
Lymph-nodes,  122 

blood-vessels  of,  124 

bronchial,  272 

distribution  of,  125 
germinal  center,  123 

hilusof,  122 
medullary  cords,  123 

nerves  of.  125 


420 


INDEX. 


Lymph-nodes,  peripheral,  125 

pulp  of,  124 

secondary  nodules,  123 

-sinus,  123 

solitary,  125 

trabeculse  of,  123 
Lymph-spaces,  adventitial,  185 

perivascular,  185 
Lymph  vessels,  121,  122 

origin  of,  121 

stomata,  122 
Lymphocyte,  140 


M. 

Macula  lutea,  353 

Malpighian  corpuscle  of  kidney,  277 
"  "         of  spleen,  126 

Mammary  glands,  335 
accessory,  336 
ampulla  of,  335 
ducts  of,  335 
nipple,  336 
secretion  of,  337 
sinus  lactiferus,  335 
Margarin  crystals,  80 
Marrow,  cells  of,  140 

elements  of,  139,  140,  141 
red,  139 
yellow,  141 
Mast-cells,  79 
Measurement,  53 
Medullary  rays,  277 

"         segments,  105 
Membrana  chorii,  313 

granulosum,  301 
limitans  iridis,  347 
limitans  olfactoria,  395 
propria,  8 1 
reticularis,  384 
tectoria,  384 
vestibularis,  379,  380 
Meissner's  plexus,  239 
Metakinesis,  62 
Metaphase,  61 
Methyl- violet,  B,  25 
Methylene-blue,  25,  39 
Microscope,  care  of,  17 
management  of,  50 
Microsomes,  56 
Microtome,  402 
Mikron,  59 
Milk,  human,  337 
Mitotic  cell- division,  60 

in  the  intestines,  232 
in  the  lymph-glands,  123 
Moist  chamber,  49 
Molecular  motion,  60 
Monaster,  62 
Mother-star,  62 
Motor  nerve-endings,  195 
Mounting,  44 

Mucous  glands,  74,  208,  221,  240 
Mucous  membranes,  structure  of,  208 
Mucous  membrane  of  the  oral  cavity,  208,  209 
Mtiller's  fluid,  21,  31 


Muscle,  156-160 

cardiac,  94 

endomysium,  156 

epimysium,  156 

perimysium,  156 

smooth,  90 

striated,  92 
Muscle-columns,  93 
Muscle-fibers,  90-95 

branched,  92 

ends  of,  92 

fibrillae  of,  93 

isolation  of,  29 

nuclei  of,  93 

pale,  94 

red,  94 

sarcolemma,  93 

smooth,  90 

striated,  92 
Myelin,  104 
Myelocytes,  140 
Myeloplaxes,  140 


N. 

Nails,  325 

elements  of,  325 

growth  of,  326 

lunuja,  326 

matrix  of,  325 

substance  of,  326 
Nail  bed,  325 
Nasal  mucous  membrane,  393 

blood-vessels  of,  397 
lymph-vessels  of,  397 
olfactory  region  of,  394 
respiratory  region  of,  393 
vestibular  region  of,  393 
Nerve-cells,  99 

of  the  first  type,  101 

of  the  second  type,  101 

processes  of,  100 
Nerve-endings,  190 

end-bulbs,  192 

in  epithelium,  190 

in  striated  muscle,  195 

motor,  195 

tactile-cells,  191 

tactile  corpuscles,  192 

sensory,  190 
Nerve-felt,  102 
Nerve-fibers,  102 

axis-cylinder,  104 

bundles  of,  186 

medullary  sheath  of,  104 

medullated,  103 

neurilemma,  105 

nodes  of,  105 

nonmedullated,  103 
Nerve-process,  100 
Nerve-trunks,  185 

blood-vessels  of,  187  - 

cerebro-spinal,  185 

endoneurium,  1 86 

epineurium,  185 

fiber  sheath,  1 86 


INDEX. 


421 


Nerve-trunks,  lymphatics  of,  187 

perineurium,  185 

sympathetic,  187 
Net  knots,  57 
Neuroblasts,  97 
Neurodendron,  97 
Neuro-epithelium,  66 

of  ear,  378,  381 

of  nose,  394 

of  retina,  352 

of  tongue,  398 

Neuroglia,  106,  170,  175,  180 
Neuron,  97 
Neuropilem,  102 
Neuroplasm,  104 
Nitric  acid,  20,  31 
Node  of  Ranvier,  105 
Normal  salt  solution,  19 
Nuclear  fluid,  57 

"        spindle,  62 
Nuclein,  57 
Nucleolus,  57 
Nucleus,  57 

structure  of,  57,  64 
Nuhn's  glands,  222 

O. 

Ocular-micrometer,  53 
Odontoblasts,  212 
Olfactory  organ,  393 

mucous  membrane  of,  394 
nerves  of,  396 
sustentacular  cells  of,  394 
tunica  propria  of,  395 

basal  cells,  395 

buds,  397 

cells,  394 

glands,  395 

membrana  limitans  olfactoria,  395 
Omentum,  254 
Ora  serrata,  355 
Orcein,  25,  40 
Organ  of  Giraldes,  295 
Osmic  acid,  22,  32 
Osmio-bichromate  mixture,  21,  41 
Ossification,  147 

center  of,  147 

endochondral,  147 

metaplastic  mode  of,  150 

neoplastic  mode  of,  150 

perichondral,  147 

periosteal,  147 
Osteoblasts,  149 
Osteoclasts,  152 
(jloconia,  378 
Otoliths,  378 
Ova  of  frog,  320 
Ovary,  298 

blood-vessels  of,  302 

corpus  luteum,  301 

germinal  epithelium,  299 

lymph-vessels  of,  302 

nerves  of,  302 

primitive  follicles,  299 

stroma  of,  298  • 


Ovary,  tunica  albuginea  of,  298 
vesicular  follicles,  300 

Oviduct,  303 

Ovula  Nabothi,  306 

Ovum,  299 

corona  radiata,  301 
dentoplasm,  300 
germinal  spot,  300 
germinal  vesicle,  300 
vitellus,  300 
zona  pellucida,  300 


P. 


Pacchionian  bodies,  184 
Pacinian  corpuscles,  193 
Pal's  mixture,  24 
Pancreas,  241 

zymogen  granules  of,  242 
Panniculus  adiposus,  321 
Papillae,  circumvallate,  219 

filiform,  218 

foliate,  220 

fungiform,  218 
Papillary  body,  367 
Paradidymis,  295 
Paraffin -chloroform  mixture,  404 
Paranuclein,  57 
Paranucleus,  58 
Paraxon,  101 
Paroophoron,  303 
Parotid  gland,  240 
Pelvis  of  kidney,  284 
Penis,  296 

arteries  of,  297 

corpora  cavernosa,  296 

corpus  spongiosum,  297 

erectile  tissue  of,  297 

helicine  arteries,  297 

tunica  albuginea  of,  296 

veins  of,  297 
Perichondrium,  145 
PerichoroMal  space,  364 
Periosteum,  137,  141 
Peritoneum,  254 
Peri  vascular  spaces,  185 
Permanent  preparations,  storing  of,  49 
Peyer's  patches,  125,  235 
Pharyngeal  tonsil,  223 
Pharynx,  223 
Pia,  183 
Picric  acid,  21 
Picrocarmine,  24,  38 
Picrosulphuric  acid,  21,  31 
Pigmentation  of  skin,  324 

theories  of,  324 
Pineal  body,  182 
Pituitary  body,  182 
Placenta,  311 

amnion,  313 

arteries  of,  314 

blood-vessel  system  of,  314 

canalized  fibrin,  315 

cell-patches,  315 

chorion  frondosum,  311 


422 


INDEX. 


Placenta,  chorionic  villi,  313 

decidua  serotina,  313 

fcetalis,  311 

intervillous  spaces,  314 

septa  of,  315 

syncytium,  315 

uterina,  311,  315 
Plasma-cells,  79 
Plastin,  56 

Platinum-acetic-osmic  mixture,  22,  33 
Platinum  chlorid,  22 
Pleura,  271 
Plexus  choroidei,  184 
climbing,  181 
epilemmal,  243 
myentericus,  238 
myospermaticus,  295 
submucosus,  239 
Polar  field,  61 
Polar  radiation,  62 
Potash  lye,  22 
Potassium  bichromate,  20 

"         permanganate,  24 
Prickle-cells,  68 
Prophase,  60 
Prostate  body,  296 
Prostatic  crystals,  296 
Protoplasm,  56 
Pyramids  of  Ferrein,  277 
Pyrenin,  57 

R. 

Radial  fibers  of  Miiller,  349 
Reagents,  19 

Reissner's  membrane,  379 
Remak's  fibers,  103 
Renal  corpuscles,  277 
Rete  testis,  289 
Retia  mirabilia,  122 
Retina,  348 

cerebral  layer,  350 

cone-visual  cells,  352 

elements  of,  371 

fovea,  353 

macula,  353 

neuro-epithelial  layer,  352 

ora  serrata,  355 

pigmented  epithelium  of,  357 

rod-visual  cells,  352 
Rhizoneurons,  164 
Ribbon-cutting,  407 
Rod-fibers,  352 
Rod-granules,  352 


S. 

Sacculus,  377 
Safranin,  25,  38 
Salivary  corpuscles,  221 
"        glands,  239 

blood-vessels  of,  243 
demilunes,  240 
lymph-vessels  of,  243 
mixed,  240 
mucous,  240 


Salivary  glands,  nerves  of,  243 

serous,  240 

Salt  solution,  normal,  19 
Sarcolemma,  93 
Sarcoplasm,  95 
Sarcostyles,  93 
Sarcous  elements,  93 
Schlussleisten,  68 
Sclera,  344 
Sebaceous  glands,  331 

distribution  of,  332 
secretion  of,  332 
Sebum,  332 

Secretory  capillaries,  74,  228,  247 
Sections,  preservation  of,  409 
Sectioning,  34,  407 

celloidin  objects,  408 

obstacles  in,  and  their  remedy,  407 

paraffin  objects,  407 
Semen,  292 

elements  of,  293,  318 
Semicircular  canals,  377 
ampullae  of,  377 

cristse  acusticse,  377 
Seminal  filaments  of  frog,  319 
Seminiferous  tubules,  289 
Septula  medullaria,  163 
Sertoli's  columns,  291 
Sharpey's  fibers,  85,  142 
Silver  nitrate,  22,  40 
Sinus  lactiferus,  335 
Sister  loops,  62 
Skin,  32i,337 

arrector  pili,  326 

blood-vessels  of,  333 

coil-glands,  332 

color  of,  324 

corium,  321 

dermis,  321 

epidermis,  321,  323 

glands  of,  331 

hair,  326 

hair-follicles,  326 

keratohyalin  granules,  323 

lymph-vessels  of,  333 

nails,  325 

nerves  of,  333 

panniculus  adiposus,  321 

papillae  of,  321 

pigment  of,  324 

sebaceous  glands,  331 

stratum  corneum,  323 

stratum  germinativum,  323 

stratum  granulosum,  323 

stratum  lucidum,  323 

stratum  papillare,  321 

stratum  reticulare,  321 

stratum  subcutaneum,  321 

striated  muscle-fibers  of,  323 
Slides,  18 
Smooth  muscle,  90 
Sodium  carminate,  25 

"        hyposulphite,  21 
Solitary  follicles,  324 
Spaces  of  Fonta-ia,  348 
"      of  Nuel,  384 


INDEX. 


423 


Spatia  zonularia,  363 
Spatium  interfasciale,  364 
Spermatids,  292 
Spermatogenesis,  291 
Spermatozoa,  293 
Spinal  cord,  162, 199 

anterior  column,  162 

anterior  cornua,  162 

anterior  gray  commissure,  163 

anterior  median  fissure,  162 

anterior  roots  of  nerves  of,  162 

central  canal,  163 

collateral  fibers,  166,  168 

column-cells,  164,  165 

column  of  Burdach,  162 

column  of  Clark,  163 

column  of  Goll,  162 

commissure-cells,  165 

conus  medullaris,  164 

Deiters's  cells,  166,  171 

dorsal  nucleus,  163 

ependymal  cells,  170 

funiculus  cuneatus,  162 

funiculus  gracilis,  162 

glia-cells,  170 

Golgi's  method  of  staining,  200 

gray  substance  of,  162 

internal  cells,  164,  166 

lateral  column,  162 

lateral  cornua,  162 

motor  nerve-cells,  164 

nerve-fibers  of,  167 

neuroglia,  170 

posterior  column,  162 

posterior  cornua,  162 

posterior  gray  commissure  of,  163 

posterior  roots  of  nerves  of,  162 

posterior  septum,  162 

plurifunicular  cells,  166 

reticular  process,  163 

septula  medullaria,  163 

stem-fibers,  166 

substantia  gelatinosa,  163 

substantia  grisea  centralis,  163 

white  commissure,  162 

white  substance  of,  168 

zona  spongiosa,  163 

zona  terminalis,  163 
Spiral  organ,  381 
Spleenj  126 

blood-vessels  of,  128 

capsule  of,  126 

intermediate  lacunae,Ni29 

lymphatics  of,  129 

Malpighian  corpuscles  of,  126 

pulp  of,  127 

trabeculne  of,  126 
Spleen-follicle,  126 
Spongioplasm,  56 
Stage-micrometer,  53 
Staining,  35 

bulk,  37 

diffuse,  36 

double,  37 

gold,  43 

mucus,  39 


Staining,  nuclear,  36 
silver,  40 
triple,  40 

under  the  cover-glass,  48 
Stomach,  224,  258 

Auerbach's  plexus,  238 
blood-vessels  of,  236 
epithelium  of,  224 
glands  of,  225 
lymph-vessels  of,  238 
Meissner's  plexus,  239 
mucous  membrane  of,  224 
muscular  tissue  of,  229 
nerves  of,  238 
Striated  muscle,  92 
Sublingual  gland,  240 
Submaxillary  glands,  240 
Substantia  adamatina,  211 
compacta,  137 
eburnea,  210 
gelatinosa,  163 
grisea  centralis,  163 
lentis,  358 
spongiosa,  137 
Sudoriparous  glands,  332 
Supporting  tissues,  76 
Suprarenal  body,  196 

blood-vessels  of,  197 
nerves  of,  197 
zona  fasciculata,  196 
zona  glomerulosa,  196 
zona  reticularis,  196 
Sutures,  143 
Sweat-glands,  332 
Syncytium,  315 
Synovia,  145 

Synovial  membranes,  144 
villi  of,  145 


T. 

Tactile  cells,  191,  192 
Tapetum  cellulosum,  345 

"         fibrosum,  345 
Tarsus,  366 
Taste-buds,  220,  399 

gustatory  cells,  399 

nerves  of,  401 

orientation  of,  400,  401 

taste-pore,  399 

tegmental  cells,  399 
Tear-glands,  36.7 

accessory,  367 
Teasing,  28 
Teeth,  209-255 

blood-vessels  of,  210,  212 

cementum,  210,  212 

crown,  210 

dental  bulb,  213 

dental  furrow,  214 

dental  papilla,  213 

dental  ridge,  213 

dental  sack,  217 

dentinal  fibers,  211,  212 

dentinal  globules,  211 


424 

Teeth,  dentinal  pulp,  210 

dentinal  sheath,  211 

dentinal  tubules,  21 1 

dentine,  210 

development  of,  212 

enamel,  211 

enamel  cuticle,  212 

enamel  organ,  214 

enamel  prisms,  21 1 

epithelial  sheath,  215 

fang,  210 

interglobular  spaces,  211 

isthmus,  214 

nerves  of,  212 

odontoblasts,  215 
Telas  choroideae,  184 
Tendon,  158 

cells  of,  158 
Tendon-sheath,  159 
Tendon-spindle,  160 
Tenon's  space,  364 
Terminal  bars,  68 

"        bronchioles,  267 

"        vesicles,  267 
Testicle,  289,  318 

blood-vessels  of,  292 

cells  of,  291 

ducts  of,  293 

elements  of,  291,  318 

lobules  of,  289 

lymph -vessels  of,  292 

mediastinum  testis,  289 

nerves  of,  292 

rete  testis,  289 

secretion  of,  292 

seminiferous  tubules,  289 

Sertoli's  columns,  291 

tubuli  recti,  289,  292 

tunica  albuginea  of,  289 

tunica  vasculosa  of,  289 
Thymus  body,  273 

blood-vessels  of,  274 

corpuscles  of,  274 
Thyro-glossal  duct,  272 
Thyroid  gland,  272 

colloid  substance  of,  273 
duct  of,  272 
Tissue  juices,  86 
Tissues,  55 

animal,  56 

vegetative,  56 
Tongue,  217,  257 

blood-vessels  of,  222 

glands  of,  221 

lymph-follicles  of,  220 

lymph-vessels  of,  222 

mucosa  of,  218 

muscles  of,  217 

nerves  of,  222 

papillae  of,  218 
Tonsils,  223 
Trachea,  267 
Trachoma  glands,  367 
Transitional  epithelium,  284 
Triacid  solution,  133 
Tympanum,  388 


INDEX. 

Top-plate,  65,  383 


U. 


Ureters,  284 

Urethra,  285 

Urinary  bladder,  285 

Urogenital  sinus,  286 

Uterus,  304 

blood-vessels  of,  306 
cervix,  306 
glands  of,  306 
lymph- vessels  of,  311 
mucosa  of  gravid,  308 
mucosa  of  menstruating,  306 
mucosa  of  virgin  resting,  305 
mucous  crypts,  306 
nerves  of,  311 
ovula  Nabothi,  306 

Utricle,  377 


V. 

Vagina,  317 

Valvulse  conniventes,  229 
Vasoformative  cells,  131 
Vater's  corpuscles,  193 
Veins,  114 

valves  of,  116 

Ventricle  of  Morgagni,  266 
Vesuvin,  25 

Vicq  d'Azyr's  bundle,  175 
Villi  of  small  intestine,  230 

of  placenta,  314 

synovial,  145 
Visual  purple,  352 
Vitellus,  300 
Vitreous  body,  341,  360 
Vocal  cords,  267 
Volkmann's  canals,  139 
Voluntary  muscle,  92 


W. 

Wagner  and  Meissner's  corpuscles,  194 
Wandering  cells,  80 

hematogenetic,  80 

histogenetic,  80 
Westphal's  alum-carmine  dahlia,  25 


Xylol,  23 
Xylol-balsam,  23 


Zellknoten,  315 
Zenker's  fluid,  21,  31 
Zona  pectinata,  382 
"     pellucida,  300 
"     perforata,  381 
"     tecta,  382 
Zone  of  Zinn,  360 
Zonula  ciliaris,  360 

granules,  242 
S? 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW 


AN     INITIAL    FINE    OF    25    CENTS 

WILL  BE  ASSESSED  FOR  FAILURE  TO  RETURN 
THIS  BOOK  ON  THE  DATE  DUE.  THE  PENALTY 
WILL  INCREASE  TO  SO  CENTS  ON  THE  FOURTH 
DAY  AND  TO  $1.OO  ON  THE  SEVENTH  DAY 
OVERDUE. 


MAR  26  W33 
Art  20  1933 

• 

OCT 
MAY    3  1935 


^ 

MAY  3     1938 
JUN  5     1943 


LEY  UBRARIES 


J?7 

m  r*"- 


I!**' 

G 
UNIVERSITY  OF  CALIFORNIA  LIBRARY 


I 


